fix(admin): report unreachable info members as unknown with balanced drive counts (#4607)

fix(admin): report unreachable info members as `unknown` with balanced drive counts `GET /rustfs/admin/v3/info` synthesizes an entry for every peer, but a peer whose properties RPC failed below the offline threshold with no cached snapshot was reported as `initializing` with an empty drive list. That drive list being empty meant its drives disappeared from the backend summary entirely, so `onlineDisks + offlineDisks` no longer equaled `totalDrivesPerSet` (an operator sees `onlineDisks: 3, offlineDisks: 0` for a 4-drive set), and `initializing` is a misleading state for a member that has been running for hours — it reads like a node was ejected when nothing is wrong (upstream rustfs/rustfs#4566). Changes: - madmin: add `ItemState::Unknown` ("unknown") and an `unknownDisks` bucket on `ErasureBackend` (serde `default`, so older payloads still deserialize). - ecstore diagnostics: `get_online_offline_disks_stats` now returns a third `unknown` bucket instead of folding those drives into `offline`, keeping `online + offline + unknown == totalDrivesPerSet`. - ecstore notification_sys: a probe miss below the failure threshold with no cache is now reported as `unknown` (not `initializing`) and carries the host's drives from the pool topology (tagged `unknown`) so the summary stays balanced; drive synthesis is factored into `synthesized_disks(host, endpoints, state)`, shared by the offline and unknown paths. Tracked in rustfs/backlog#1049 (P1-A + P0-A). Co-authored-by: heihutu <heihutu@gmail.com>
2026-07-26 08:18:18 +00:00 · 2026-07-09 12:50:20 +08:00
parent d8c32d3754
commit cb977c4c5a
3 changed files with 435 additions and 53 deletions
@@ -21,7 +21,8 @@ use crate::data_usage::load_data_usage_cache;
 use crate::storage_api_contracts::admin::StorageAdminApi;
 use rustfs_common::heal_channel::DriveState;
 use rustfs_madmin::{
-    BackendDisks, Disk, ErasureSetInfo, ITEM_INITIALIZING, ITEM_OFFLINE, ITEM_ONLINE, InfoMessage, MemStats, ServerProperties,
+    BackendDisks, Disk, ErasureSetInfo, ITEM_INITIALIZING, ITEM_OFFLINE, ITEM_ONLINE, ITEM_UNKNOWN, InfoMessage, MemStats,
+    ServerProperties,
 };
 use rustfs_protos::{
    models::{PingBody, PingBodyBuilder},
@@ -276,7 +277,7 @@ pub async fn get_server_info(get_pools: bool) -> InfoMessage {
        for server in servers.iter() {
            all_disks.extend(server.disks.clone());
        }
-        let (online_disks, offline_disks) = get_online_offline_disks_stats(&all_disks);
+        let (online_disks, offline_disks, unknown_disks) = get_online_offline_disks_stats(&all_disks);

        let after5 = OffsetDateTime::now_utc();

@@ -285,6 +286,7 @@ pub async fn get_server_info(get_pools: bool) -> InfoMessage {
            backend_type: rustfs_madmin::BackendType::ErasureType,
            online_disks: online_disks.sum(),
            offline_disks: offline_disks.sum(),
+            unknown_disks: unknown_disks.sum(),
            standard_sc_parity: backend_info.standard_sc_parity,
            rr_sc_parity: backend_info.rr_sc_parity,
            total_sets: backend_info.total_sets,
@@ -318,19 +320,32 @@ pub async fn get_server_info(get_pools: bool) -> InfoMessage {
    }
 }

-fn get_online_offline_disks_stats(disks_info: &[Disk]) -> (BackendDisks, BackendDisks) {
+/// Classify every drive into online / offline / unknown buckets.
+///
+/// `unknown` holds drives synthesized for a member whose properties RPC could
+/// not be answered this cycle but which is not confirmed offline. Keeping them
+/// out of the `offline` bucket means a transient probe miss no longer inflates
+/// the offline count for a healthy member, while `online + offline + unknown`
+/// still sums to the pool's total drive count (rustfs/backlog#1049).
+fn get_online_offline_disks_stats(disks_info: &[Disk]) -> (BackendDisks, BackendDisks, BackendDisks) {
    let mut online_disks: HashMap<String, usize> = HashMap::new();
    let mut offline_disks: HashMap<String, usize> = HashMap::new();
+    let mut unknown_disks: HashMap<String, usize> = HashMap::new();

    for disk in disks_info {
        let ep = &disk.endpoint;
        offline_disks.entry(ep.clone()).or_insert(0);
        online_disks.entry(ep.clone()).or_insert(0);
+        unknown_disks.entry(ep.clone()).or_insert(0);
    }

    for disk in disks_info {
        let ep = &disk.endpoint;
        let state = &disk.state;
+        if *state == ITEM_UNKNOWN {
+            *unknown_disks.get_mut(ep).expect("endpoint should be in disk map") += 1;
+            continue;
+        }
        if *state != DriveState::Ok.to_string() && *state != DriveState::Unformatted.to_string() {
            *offline_disks.get_mut(ep).expect("endpoint should be in disk map") += 1;
            continue;
@@ -345,8 +360,11 @@ fn get_online_offline_disks_stats(disks_info: &[Disk]) -> (BackendDisks, Backend
        }
    }

-    if disks_info.len() == (root_disk_count + offline_disks.values().sum::<usize>()) {
-        return (BackendDisks(online_disks), BackendDisks(offline_disks));
+    // When every non-offline, non-unknown drive is a root mount, leave the
+    // online tally as-is instead of demoting all of them (matches the prior
+    // behavior; the unknown bucket is simply carried through untouched).
+    if disks_info.len() == (root_disk_count + offline_disks.values().sum::<usize>() + unknown_disks.values().sum::<usize>()) {
+        return (BackendDisks(online_disks), BackendDisks(offline_disks), BackendDisks(unknown_disks));
    }

    for disk in disks_info {
@@ -357,7 +375,7 @@ fn get_online_offline_disks_stats(disks_info: &[Disk]) -> (BackendDisks, Backend
        }
    }

-    (BackendDisks(online_disks), BackendDisks(offline_disks))
+    (BackendDisks(online_disks), BackendDisks(offline_disks), BackendDisks(unknown_disks))
 }

 async fn get_pools_info(all_disks: &[Disk]) -> Result<HashMap<i32, HashMap<i32, ErasureSetInfo>>> {
@@ -413,8 +431,45 @@ mod tests {
    use serial_test::serial;

    use crate::runtime::sources as runtime_sources;
+    use rustfs_madmin::{Disk, ITEM_OFFLINE, ITEM_UNKNOWN};

-    use super::{get_local_server_property, get_server_info};
+    use super::{get_local_server_property, get_online_offline_disks_stats, get_server_info};
+
+    fn disk_with_state(endpoint: &str, state: &str) -> Disk {
+        Disk {
+            endpoint: endpoint.to_string(),
+            state: state.to_string(),
+            ..Default::default()
+        }
+    }
+
+    #[test]
+    fn disk_stats_split_unknown_into_its_own_bucket() {
+        // A member whose properties RPC could not be answered contributes
+        // drives tagged `unknown`. They must land in the unknown bucket, not
+        // inflate `offline`, and the three buckets must still account for every
+        // drive so the summary stays balanced (rustfs/backlog#1049).
+        //
+        // A live drive reports the DriveState string "ok"; only "ok"/"unformatted"
+        // count as online.
+        let disks = vec![
+            disk_with_state("http://n1:9000/data", "ok"),
+            disk_with_state("http://n2:9000/data", "ok"),
+            disk_with_state("http://n3:9000/data", ITEM_OFFLINE),
+            disk_with_state("http://n4:9000/data", ITEM_UNKNOWN),
+        ];
+
+        let (online, offline, unknown) = get_online_offline_disks_stats(&disks);
+
+        assert_eq!(online.sum(), 2, "the two healthy drives are online");
+        assert_eq!(offline.sum(), 1, "only the confirmed-offline drive is offline");
+        assert_eq!(unknown.sum(), 1, "the unreachable member's drive is unknown, not offline");
+        assert_eq!(
+            online.sum() + offline.sum() + unknown.sum(),
+            disks.len(),
+            "online + offline + unknown must equal the total drive count"
+        );
+    }

    #[serial]
    #[tokio::test]
@@ -14,6 +14,7 @@

 use crate::cluster::rpc::PeerRestClient;
 use crate::diagnostics::admin_server_info::get_commit_id;
+use crate::disk::DiskAPI;
 use crate::error::{Error, Result};
 use crate::layout::endpoints::EndpointServerPools;
 use crate::runtime::sources as runtime_sources;
@@ -46,6 +47,10 @@ struct PeerAdminCache {
    last_server_info: Option<ServerProperties>,
    storage_failures: u32,
    server_failures: u32,
+    /// When the last successful server_info probe landed. Used to stop a stale
+    /// cached `online` snapshot from being served indefinitely while a peer is
+    /// actually down (rustfs/backlog#1049 P2).
+    last_server_success: Option<SystemTime>,
 }

 impl PeerAdminCache {
@@ -55,10 +60,16 @@ impl PeerAdminCache {
            last_server_info: None,
            storage_failures: 0,
            server_failures: 0,
+            last_server_success: None,
        }
    }
 }

+/// A cached `online` snapshot older than this is no longer trusted on a probe
+/// failure: rather than reporting a stale `online`, the member falls through to
+/// the live unknown/degraded/offline classification (rustfs/backlog#1049 P2).
+const SERVER_INFO_CACHE_MAX_AGE: Duration = Duration::from_secs(60);
+
 lazy_static! {
    pub static ref GLOBAL_NOTIFICATION_SYS: OnceLock<NotificationSys> = OnceLock::new();
 }
@@ -346,25 +357,55 @@ impl NotificationSys {
            let endpoints = endpoints.clone();
            let cache = self.peer_admin_caches.get(idx);
            futures.push(async move {
-                if let Some(client) = client {
-                    let host = client.host.to_string();
-                    match timeout(peer_timeout, client.server_info()).await {
-                        Ok(Ok(info)) => {
-                            update_server_info_cache(cache, &host, &info);
-                            info
-                        }
-                        Ok(Err(err)) => {
-                            warn!("peer {} server_info failed: {}", host, err);
-                            handle_server_info_failure(cache, &host, &endpoints)
-                        }
-                        Err(_) => {
-                            warn!("peer {} server_info timed out after {:?}", host, peer_timeout);
-                            client.evict_connection().await;
-                            handle_server_info_failure(cache, &host, &endpoints)
-                        }
+                // `peer_clients` comes from `new_clients`, which only ever pushes
+                // `Some(client)` (local hosts are excluded, not slotted as
+                // `None`), so this branch is unreachable in practice. Kept as a
+                // defensive fallback: report an explicit `unknown` state rather
+                // than a blank `default()` entry, so it can never contribute a
+                // hollow row to `servers[]` (rustfs/backlog#1049 P3).
+                let Some(client) = client else {
+                    return ServerProperties {
+                        state: ItemState::Unknown.to_string().to_owned(),
+                        ..Default::default()
+                    };
+                };
+                let host = client.host.to_string();
+
+                // First attempt. A single evicted or half-open internode channel
+                // is enough to fail one probe and, before retrying, would drop
+                // the member to unknown/offline for this whole snapshot. So on any
+                // first-attempt failure we evict the channel and re-dial once
+                // before falling back (rustfs/backlog#1049, P1-B).
+                match timeout(peer_timeout, client.server_info()).await {
+                    Ok(Ok(info)) => {
+                        update_server_info_cache(cache, &host, &info);
+                        return info;
+                    }
+                    Ok(Err(err)) => debug!("peer {host} server_info failed (attempt 1/2): {err}"),
+                    Err(_) => debug!("peer {host} server_info timed out (attempt 1/2) after {peer_timeout:?}"),
+                }
+
+                // Drop the suspect channel so the retry re-dials on a fresh
+                // connection instead of reusing the bad one.
+                client.evict_connection().await;
+
+                // Second and final attempt on the fresh channel.
+                match timeout(peer_timeout, client.server_info()).await {
+                    Ok(Ok(info)) => {
+                        update_server_info_cache(cache, &host, &info);
+                        info
+                    }
+                    Ok(Err(err)) => {
+                        warn!("peer {host} server_info failed after retry: {err}");
+                        let health = peer_disk_health(&host).await;
+                        handle_server_info_failure(cache, &host, &endpoints, health.as_ref())
+                    }
+                    Err(_) => {
+                        warn!("peer {host} server_info timed out after retry ({peer_timeout:?})");
+                        client.evict_connection().await;
+                        let health = peer_disk_health(&host).await;
+                        handle_server_info_failure(cache, &host, &endpoints, health.as_ref())
                    }
-                } else {
-                    ServerProperties::default()
                }
            });
        }
@@ -1047,7 +1088,7 @@ fn handle_peer_failure(
            );
        }
        return Some(StorageInfo {
-            disks: get_offline_disks(host, endpoints),
+            disks: synthesized_disks(host, endpoints, ItemState::Offline),
            ..Default::default()
        });
    }
@@ -1080,15 +1121,91 @@ fn update_storage_info_cache(cache: Option<&Mutex<PeerAdminCache>>, host: &str,
    c.storage_failures = 0;
 }

-/// Handle a peer failure for server_info: return cached data if available,
-/// or mark offline only after consecutive failures exceed the threshold.
+/// Independent liveness evidence for a peer, gathered from the local disk-health
+/// heartbeat rather than the admin RPC path. `any_online` is true when at least
+/// one of the peer's drives is still answering the ~15s health check; `disks`
+/// carries a per-drive entry (state `"ok"` when online, `"offline"` when the
+/// heartbeat marks it faulty) so a `degraded` member's drives are counted for
+/// real. See rustfs/backlog#1049 (P0-B).
+struct PeerDiskHealth {
+    any_online: bool,
+    disks: Vec<rustfs_madmin::Disk>,
+}
+
+/// Consult the local disk-health state for `host` without issuing any RPC.
+///
+/// On the aggregating node a peer's drives are remote-disk handles whose
+/// `is_online()` is a pure atomic read of the heartbeat tracker (independent of
+/// the admin `server_info` RPC that just failed). Returns `None` when the store
+/// is not initialized or the host owns no drives in the topology.
+async fn peer_disk_health(host: &str) -> Option<PeerDiskHealth> {
+    let store = runtime_sources::object_store_handle()?;
+
+    let mut disks = Vec::new();
+    let mut any_online = false;
+    for sets in store.pools.iter() {
+        for set in sets.disk_set.iter() {
+            let guard = set.disks.read().await;
+            for (idx, slot) in guard.iter().enumerate() {
+                let Some(ep) = set.set_endpoints.get(idx) else {
+                    continue;
+                };
+                if host != ep.host_port() {
+                    continue;
+                }
+                let online = match slot {
+                    Some(disk) => disk.is_online().await,
+                    None => false,
+                };
+                any_online |= online;
+                // A live drive is counted online via the DriveState "ok" string;
+                // a faulty one is counted offline. This keeps a degraded member's
+                // drives in the real online/offline buckets.
+                disks.push(rustfs_madmin::Disk {
+                    endpoint: ep.to_string(),
+                    state: if online {
+                        rustfs_common::heal_channel::DriveState::Ok.to_string()
+                    } else {
+                        ItemState::Offline.to_string().to_owned()
+                    },
+                    pool_index: ep.pool_idx,
+                    set_index: ep.set_idx,
+                    disk_index: ep.disk_idx,
+                    ..Default::default()
+                });
+            }
+        }
+    }
+
+    if disks.is_empty() {
+        None
+    } else {
+        Some(PeerDiskHealth { any_online, disks })
+    }
+}
+
+/// Handle a peer failure for server_info: return cached data if available, or
+/// classify the member as `unknown` / `degraded` / `offline` depending on how
+/// many consecutive probes have failed and whether the peer's drives are still
+/// answering the local disk-health heartbeat.
+///
+/// - Below the failure threshold with no cached snapshot: `unknown` (probe
+///   missed this cycle but the member is not confirmed down).
+/// - At/after the threshold with drives still online: `degraded` (the admin RPC
+///   is stuck but the node is alive and serving data) — this is what stops a
+///   healthy node from rotating through a false `offline` (rustfs/backlog#1049).
+/// - At/after the threshold with drives also offline: `offline` (confirmed).
+///
+/// Synthesized entries always carry one drive per endpoint so the pool's drive
+/// totals stay balanced.
 fn handle_server_info_failure(
    cache: Option<&Mutex<PeerAdminCache>>,
    host: &str,
    endpoints: &EndpointServerPools,
+    peer_health: Option<&PeerDiskHealth>,
 ) -> ServerProperties {
    let Some(cache) = cache else {
-        return initializing_server_properties(host);
+        return unknown_server_properties(host, endpoints);
    };

    let mut c = match cache.lock() {
@@ -1103,17 +1220,51 @@ fn handle_server_info_failure(
    if let Some(ref cached) = c.last_server_info
        && c.server_failures < CONSECUTIVE_FAILURE_THRESHOLD
    {
+        if cached_snapshot_is_fresh(c.last_server_success) {
+            debug!(
+                event = "peer_probe_failure",
+                peer = host,
+                consecutive_failures = c.server_failures,
+                threshold = CONSECUTIVE_FAILURE_THRESHOLD,
+                "peer server_info probe failed; returning cached state until the offline threshold is reached"
+            );
+            return cached.clone();
+        }
+        // The cached snapshot is too old to keep reporting as `online`; fall
+        // through to the live unknown/degraded/offline classification below
+        // instead of masking a down peer with a stale success (P2).
        debug!(
-            event = "peer_probe_failure",
+            event = "peer_cache_stale",
            peer = host,
-            consecutive_failures = c.server_failures,
-            threshold = CONSECUTIVE_FAILURE_THRESHOLD,
-            "peer server_info probe failed; returning cached state until the offline threshold is reached"
+            max_age_secs = SERVER_INFO_CACHE_MAX_AGE.as_secs(),
+            "cached server_info snapshot is stale; reclassifying from live signals instead of reporting stale online"
        );
-        return cached.clone();
    }

    if c.server_failures >= CONSECUTIVE_FAILURE_THRESHOLD {
+        // Drives still answering the heartbeat: the node is alive, only its
+        // admin surface is unreachable — report `degraded`, not `offline`, so a
+        // stuck admin path does not read as an ejected node.
+        if let Some(health) = peer_health.filter(|h| h.any_online) {
+            if c.server_failures == CONSECUTIVE_FAILURE_THRESHOLD {
+                warn!(
+                    event = "peer_marked_degraded",
+                    peer = host,
+                    consecutive_failures = c.server_failures,
+                    threshold = CONSECUTIVE_FAILURE_THRESHOLD,
+                    "peer admin server_info keeps failing but its drives are online; reporting degraded (not offline)"
+                );
+            } else {
+                debug!(
+                    event = "peer_still_degraded",
+                    peer = host,
+                    consecutive_failures = c.server_failures,
+                    "peer admin server_info still failing while its drives remain online"
+                );
+            }
+            return degraded_server_properties(host, &health.disks);
+        }
+
        // Log the transition exactly once (at the crossing) so the console's
        // "node offline" verdict has a matching WARN in the observer's logs
        // (rustfs/backlog#888: nodes were marked offline with no log naming
@@ -1139,7 +1290,7 @@ fn handle_server_info_failure(
        return offline_server_properties(host, endpoints);
    }

-    initializing_server_properties(host)
+    unknown_server_properties(host, endpoints)
 }

 fn update_server_info_cache(cache: Option<&Mutex<PeerAdminCache>>, host: &str, info: &ServerProperties) {
@@ -1163,13 +1314,31 @@ fn update_server_info_cache(cache: Option<&Mutex<PeerAdminCache>>, host: &str, i
        );
    }
    c.last_server_info = Some(info.clone());
+    c.last_server_success = Some(SystemTime::now());
    c.server_failures = 0;
 }

-fn initializing_server_properties(host: &str) -> ServerProperties {
+/// Whether a cached server_info snapshot is recent enough to still report as
+/// `online` on a probe failure. A missing timestamp means no age information is
+/// available (e.g. a snapshot set without going through the success path in a
+/// test); such a snapshot is treated as fresh to preserve the prior behavior,
+/// while a clock that went backwards is treated as stale. See P2 in
+/// rustfs/backlog#1049.
+fn cached_snapshot_is_fresh(last_success: Option<SystemTime>) -> bool {
+    match last_success {
+        Some(at) => at.elapsed().map(|age| age < SERVER_INFO_CACHE_MAX_AGE).unwrap_or(false),
+        None => true,
+    }
+}
+
+/// A member that could not be probed this cycle and is not confirmed down.
+/// Carries the endpoint's drives (marked `unknown`) so the pool's drive totals
+/// stay balanced instead of the member's drives vanishing from the summary.
+fn unknown_server_properties(host: &str, endpoints: &EndpointServerPools) -> ServerProperties {
    ServerProperties {
        endpoint: host.to_string(),
-        state: ItemState::Initializing.to_string().to_owned(),
+        state: ItemState::Unknown.to_string().to_owned(),
+        disks: synthesized_disks(host, endpoints, ItemState::Unknown),
        ..Default::default()
    }
 }
@@ -1180,20 +1349,37 @@ fn offline_server_properties(host: &str, endpoints: &EndpointServerPools) -> Ser
        version: get_commit_id(),
        endpoint: host.to_string(),
        state: ItemState::Offline.to_string().to_owned(),
-        disks: get_offline_disks(host, endpoints),
+        disks: synthesized_disks(host, endpoints, ItemState::Offline),
        ..Default::default()
    }
 }

-fn get_offline_disks(offline_host: &str, endpoints: &EndpointServerPools) -> Vec<rustfs_madmin::Disk> {
-    let mut offline_disks = Vec::new();
+/// A member whose admin RPC is unreachable but whose drives are still online.
+/// Carries the per-drive health observed from the local heartbeat so the drives
+/// land in the real online/offline buckets while the member reads as degraded.
+fn degraded_server_properties(host: &str, disks: &[rustfs_madmin::Disk]) -> ServerProperties {
+    ServerProperties {
+        uptime: runtime_sources::boot_uptime_secs(),
+        version: get_commit_id(),
+        endpoint: host.to_string(),
+        state: ItemState::Degraded.to_string().to_owned(),
+        disks: disks.to_vec(),
+        ..Default::default()
+    }
+}
+
+/// Enumerate the drives a host owns from the pool topology, tagged with the
+/// given member state. Used to synthesize drive entries for a member whose
+/// properties RPC could not be answered, so summary counters stay complete.
+fn synthesized_disks(host: &str, endpoints: &EndpointServerPools, state: ItemState) -> Vec<rustfs_madmin::Disk> {
+    let mut disks = Vec::new();

    for pool in endpoints.as_ref() {
        for ep in pool.endpoints.as_ref() {
-            if (offline_host.is_empty() && ep.is_local) || offline_host == ep.host_port() {
-                offline_disks.push(rustfs_madmin::Disk {
+            if (host.is_empty() && ep.is_local) || host == ep.host_port() {
+                disks.push(rustfs_madmin::Disk {
                    endpoint: ep.to_string(),
-                    state: ItemState::Offline.to_string().to_owned(),
+                    state: state.to_string().to_owned(),
                    pool_index: ep.pool_idx,
                    set_index: ep.set_idx,
                    disk_index: ep.disk_idx,
@@ -1203,7 +1389,7 @@ fn get_offline_disks(offline_host: &str, endpoints: &EndpointServerPools) -> Vec
        }
    }

-    offline_disks
+    disks
 }

 fn aggregate_notification_failures(operation: &str, failures: Vec<String>) -> Result<()> {
@@ -1415,6 +1601,7 @@ mod tests {
            last_server_info: None,
            storage_failures: 0,
            server_failures: 0,
+            last_server_success: None,
        });
        let endpoints = EndpointServerPools::default();

@@ -1442,6 +1629,7 @@ mod tests {
            last_server_info: None,
            storage_failures: CONSECUTIVE_FAILURE_THRESHOLD - 1,
            server_failures: 0,
+            last_server_success: None,
        });
        let endpoints = EndpointServerPools::default();

@@ -1464,23 +1652,69 @@ mod tests {
            last_server_info: Some(cached_props),
            storage_failures: 0,
            server_failures: 0,
+            last_server_success: None,
        });
        let endpoints = EndpointServerPools::default();

-        let result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints);
+        let result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints, None);
        assert_eq!(result.endpoint, "peer-1");
        assert_eq!(result.state, "online");
        assert_eq!(cache.lock().unwrap().server_failures, 1);
    }

    #[test]
-    fn handle_server_info_failure_returns_initializing_before_threshold_without_cache() {
+    fn handle_server_info_failure_does_not_serve_stale_cached_online() {
+        // A single failure with a cached snapshot would normally return the
+        // cached `online`, but if that snapshot is older than the max age we
+        // must not keep reporting online — fall through to `unknown` instead of
+        // masking a possibly-down peer (rustfs/backlog#1049 P2).
+        let cached_props = ServerProperties {
+            endpoint: "peer-1".to_string(),
+            state: "online".to_string(),
+            ..Default::default()
+        };
+        let stale_at = SystemTime::now()
+            .checked_sub(SERVER_INFO_CACHE_MAX_AGE + Duration::from_secs(1))
+            .expect("test clock underflow");
+
+        let cache = Mutex::new(PeerAdminCache {
+            last_storage_info: None,
+            last_server_info: Some(cached_props),
+            storage_failures: 0,
+            server_failures: 0,
+            last_server_success: Some(stale_at),
+        });
+        let endpoints = EndpointServerPools::default();
+
+        let result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints, None);
+        assert_eq!(result.state, ItemState::Unknown.to_string());
+        assert_eq!(cache.lock().unwrap().server_failures, 1);
+    }
+
+    #[test]
+    fn cached_snapshot_freshness_respects_age_and_missing_timestamp() {
+        assert!(cached_snapshot_is_fresh(None), "no timestamp is treated as fresh");
+        assert!(cached_snapshot_is_fresh(Some(SystemTime::now())), "a just-now success is fresh");
+        let stale = SystemTime::now()
+            .checked_sub(SERVER_INFO_CACHE_MAX_AGE + Duration::from_secs(1))
+            .expect("test clock underflow");
+        assert!(!cached_snapshot_is_fresh(Some(stale)), "an old success is stale");
+    }
+
+    #[test]
+    fn handle_server_info_failure_returns_unknown_before_threshold_without_cache() {
        let cache = Mutex::new(PeerAdminCache::new());
        let endpoints = EndpointServerPools::default();

-        let result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints);
+        let result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints, None);
        assert_eq!(result.endpoint, "peer-1");
-        assert_eq!(result.state, ItemState::Initializing.to_string());
+        // A probe miss below the threshold is "unknown" (not confirmed down,
+        // and not the misleading "initializing"): rustfs/backlog#1049.
+        assert_eq!(result.state, ItemState::Unknown.to_string());
+        // The default (empty) pool has no topology entry for this host, so no
+        // drives are synthesized here; the drive-synthesis and counter-balance
+        // behavior is exercised by the get_online_offline_disks_stats tests in
+        // admin_server_info.
        assert!(result.disks.is_empty());
        assert_eq!(cache.lock().unwrap().server_failures, 1);
    }
@@ -1498,14 +1732,69 @@ mod tests {
            last_server_info: Some(cached_props),
            storage_failures: 0,
            server_failures: CONSECUTIVE_FAILURE_THRESHOLD - 1,
+            last_server_success: None,
        });
        let endpoints = EndpointServerPools::default();

-        let result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints);
+        let result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints, None);
        assert_eq!(result.state, ItemState::Offline.to_string());
        assert_eq!(cache.lock().unwrap().server_failures, CONSECUTIVE_FAILURE_THRESHOLD);
    }

+    #[test]
+    fn handle_server_info_failure_returns_degraded_when_disks_online_past_threshold() {
+        // Past the threshold but the peer's drives still answer the heartbeat:
+        // the node is alive, only its admin RPC is stuck — report degraded (with
+        // the real per-drive health), not offline (rustfs/backlog#1049 P0-B).
+        let cache = Mutex::new(PeerAdminCache {
+            last_storage_info: None,
+            last_server_info: None,
+            storage_failures: 0,
+            server_failures: CONSECUTIVE_FAILURE_THRESHOLD - 1,
+            last_server_success: None,
+        });
+        let endpoints = EndpointServerPools::default();
+        let health = PeerDiskHealth {
+            any_online: true,
+            disks: vec![rustfs_madmin::Disk {
+                endpoint: "http://peer-1:9000/data".to_string(),
+                state: "ok".to_string(),
+                ..Default::default()
+            }],
+        };
+
+        let result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints, Some(&health));
+        assert_eq!(result.state, ItemState::Degraded.to_string());
+        assert_eq!(result.disks.len(), 1);
+        assert_eq!(result.disks[0].state, "ok");
+        assert_eq!(cache.lock().unwrap().server_failures, CONSECUTIVE_FAILURE_THRESHOLD);
+    }
+
+    #[test]
+    fn handle_server_info_failure_stays_offline_when_disks_also_offline() {
+        // Past the threshold and the heartbeat also reports the drives down:
+        // this is a genuine offline, degraded must not mask it.
+        let cache = Mutex::new(PeerAdminCache {
+            last_storage_info: None,
+            last_server_info: None,
+            storage_failures: 0,
+            server_failures: CONSECUTIVE_FAILURE_THRESHOLD - 1,
+            last_server_success: None,
+        });
+        let endpoints = EndpointServerPools::default();
+        let health = PeerDiskHealth {
+            any_online: false,
+            disks: vec![rustfs_madmin::Disk {
+                endpoint: "http://peer-1:9000/data".to_string(),
+                state: ItemState::Offline.to_string().to_owned(),
+                ..Default::default()
+            }],
+        };
+
+        let result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints, Some(&health));
+        assert_eq!(result.state, ItemState::Offline.to_string());
+    }
+
    #[test]
    fn success_resets_failure_counters_independently() {
        let cache = Mutex::new(PeerAdminCache {
@@ -1513,6 +1802,7 @@ mod tests {
            last_server_info: None,
            storage_failures: 2,
            server_failures: 2,
+            last_server_success: None,
        });

        {
@@ -1537,13 +1827,14 @@ mod tests {
            }),
            storage_failures: CONSECUTIVE_FAILURE_THRESHOLD - 1,
            server_failures: 0,
+            last_server_success: None,
        });
        let endpoints = EndpointServerPools::default();

        let storage_result = handle_peer_failure(Some(&cache), "peer-1", &endpoints);
        assert!(storage_result.is_some());

-        let server_result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints);
+        let server_result = handle_server_info_failure(Some(&cache), "peer-1", &endpoints, None);
        assert_eq!(server_result.state, "online");
        assert_eq!(cache.lock().unwrap().server_failures, 1);
    }
@@ -1566,9 +1857,9 @@ mod tests {
        let storage_result = handle_peer_failure(Some(&storage_cache), "peer-1", &endpoints);
        assert!(storage_result.is_none());

-        let server_result = handle_server_info_failure(Some(&server_cache), "peer-1", &endpoints);
+        let server_result = handle_server_info_failure(Some(&server_cache), "peer-1", &endpoints, None);
        assert_eq!(server_result.endpoint, "peer-1");
-        assert_eq!(server_result.state, ItemState::Initializing.to_string());
+        assert_eq!(server_result.state, ItemState::Unknown.to_string());
    }

    #[test]
@@ -1578,12 +1869,14 @@ mod tests {
            last_server_info: None,
            storage_failures: CONSECUTIVE_FAILURE_THRESHOLD - 1,
            server_failures: 0,
+            last_server_success: None,
        });
        let server_cache = Mutex::new(PeerAdminCache {
            last_storage_info: None,
            last_server_info: None,
            storage_failures: 0,
            server_failures: CONSECUTIVE_FAILURE_THRESHOLD - 1,
+            last_server_success: None,
        });
        let endpoints = EndpointServerPools::default();

@@ -1622,7 +1915,7 @@ mod tests {
        assert!(storage_result.is_some());
        assert_eq!(storage_result.unwrap().disks[0].state, "ok");

-        let server_result = handle_server_info_failure(Some(&server_cache), "peer-1", &endpoints);
+        let server_result = handle_server_info_failure(Some(&server_cache), "peer-1", &endpoints, None);
        assert_eq!(server_result.state, "online");
    }
 }
@@ -24,6 +24,18 @@ pub enum ItemState {
    Offline,
    Initializing,
    Online,
+    /// The peer could not be probed this cycle but is not confirmed down.
+    /// Distinct from `Offline` (confirmed unreachable past the failure
+    /// threshold) and `Initializing` (genuinely still starting up): a
+    /// transient probe miss on an otherwise-healthy member must not read as
+    /// an ejection. See rustfs/backlog#1049.
+    Unknown,
+    /// The peer's admin/properties RPC keeps failing, but its drives are still
+    /// answering the independent disk-health heartbeat — the node is alive and
+    /// serving data, only its admin surface is unreachable. Reported instead of
+    /// `Offline` so a stuck admin path (e.g. a saturated scanner) is not
+    /// mistaken for an ejected node. See rustfs/backlog#1049 (P0-B).
+    Degraded,
 }

 impl ItemState {
@@ -32,6 +44,8 @@ impl ItemState {
            ItemState::Offline => "offline",
            ItemState::Initializing => "initializing",
            ItemState::Online => "online",
+            ItemState::Unknown => "unknown",
+            ItemState::Degraded => "degraded",
        }
    }

@@ -40,6 +54,8 @@ impl ItemState {
            "offline" => Some(ItemState::Offline),
            "initializing" => Some(ItemState::Initializing),
            "online" => Some(ItemState::Online),
+            "unknown" => Some(ItemState::Unknown),
+            "degraded" => Some(ItemState::Degraded),
            _ => None,
        }
    }
@@ -186,6 +202,8 @@ pub struct BackendInfo {
 pub const ITEM_OFFLINE: &str = "offline";
 pub const ITEM_INITIALIZING: &str = "initializing";
 pub const ITEM_ONLINE: &str = "online";
+pub const ITEM_UNKNOWN: &str = "unknown";
+pub const ITEM_DEGRADED: &str = "degraded";

 #[derive(Clone, Debug, Default, Serialize, Deserialize)]
 pub struct MemStats {
@@ -326,6 +344,14 @@ pub struct ErasureBackend {
    pub online_disks: usize,
    #[serde(rename = "offlineDisks")]
    pub offline_disks: usize,
+    /// Drives whose owning member could not be probed this cycle and is not
+    /// confirmed offline. Kept as a separate bucket so
+    /// `online + offline + unknown == totalDrivesPerSet` holds even while a
+    /// member is unreachable, instead of the fourth drive silently vanishing
+    /// from the totals (rustfs/backlog#1049). `#[serde(default)]` keeps older
+    /// payloads that predate this field deserializable.
+    #[serde(rename = "unknownDisks", default)]
+    pub unknown_disks: usize,
    #[serde(rename = "standardSCParity")]
    pub standard_sc_parity: Option<usize>,
    #[serde(rename = "rrSCParity")]
@@ -409,6 +435,8 @@ mod tests {
        assert_eq!(ItemState::Offline.to_string(), ITEM_OFFLINE);
        assert_eq!(ItemState::Initializing.to_string(), ITEM_INITIALIZING);
        assert_eq!(ItemState::Online.to_string(), ITEM_ONLINE);
+        assert_eq!(ItemState::Unknown.to_string(), ITEM_UNKNOWN);
+        assert_eq!(ItemState::Degraded.to_string(), ITEM_DEGRADED);
    }

    #[test]
@@ -416,6 +444,8 @@ mod tests {
        assert_eq!(ItemState::from_string(ITEM_OFFLINE), Some(ItemState::Offline));
        assert_eq!(ItemState::from_string(ITEM_INITIALIZING), Some(ItemState::Initializing));
        assert_eq!(ItemState::from_string(ITEM_ONLINE), Some(ItemState::Online));
+        assert_eq!(ItemState::from_string(ITEM_UNKNOWN), Some(ItemState::Unknown));
+        assert_eq!(ItemState::from_string(ITEM_DEGRADED), Some(ItemState::Degraded));
    }

    #[test]
@@ -1145,6 +1175,7 @@ mod tests {
            backend_type: BackendType::ErasureType,
            online_disks: 8,
            offline_disks: 0,
+            unknown_disks: 0,
            standard_sc_parity: Some(2),
            rr_sc_parity: Some(1),
            total_sets: vec![2],
@@ -1154,6 +1185,7 @@ mod tests {
        assert!(matches!(erasure_backend.backend_type, BackendType::ErasureType));
        assert_eq!(erasure_backend.online_disks, 8);
        assert_eq!(erasure_backend.offline_disks, 0);
+        assert_eq!(erasure_backend.unknown_disks, 0);
        assert_eq!(erasure_backend.standard_sc_parity.unwrap(), 2);
        assert_eq!(erasure_backend.rr_sc_parity.unwrap(), 1);
        assert_eq!(erasure_backend.total_sets.len(), 1);
@@ -1271,5 +1303,7 @@ mod tests {
        assert_eq!(ITEM_OFFLINE, "offline");
        assert_eq!(ITEM_INITIALIZING, "initializing");
        assert_eq!(ITEM_ONLINE, "online");
+        assert_eq!(ITEM_UNKNOWN, "unknown");
+        assert_eq!(ITEM_DEGRADED, "degraded");
    }
 }