- Troubleshooting Recovery
This chapter describes what to do if something goes wrong during recovery. It describes:
- the section called “ Recovering from Errors or Corruption on a Backing ldiskfs File System”
- the section called “ Recovering from Corruption in the Lustre File System”
- the section called “ Recovering from an Unavailable OST”
- the section called “ Checking the file system with LFSCK”
When an OSS, MDS, or MGS server crash occurs, it is not necessary to run e2fsck on the file system. ldiskfsjournaling ensures that the file system remains consistent over a system crash. The backing file systems are never accessed directly from the client, so client crashes are not relevant for server file system consistency.
The only time it is REQUIRED that e2fsck be run on a device is when an event causes problems that ldiskfs journaling is unable to handle, such as a hardware device failure or I/O error. If the ldiskfs kernel code detects corruption on the disk, it mounts the file system as read-only to prevent further corruption, but still allows read access to the device. This appears as error "-30" ( EROFS) in the syslogs on the server, e.g.:
Dec 29 14:11:32 mookie kernel: LDISKFS-fs error (device sdz):
ldiskfs_lookup: unlinked inode 5384166 in dir #145170469
Dec 29 14:11:32 mookie kernel: Remounting filesystem read-only
In such a situation, it is normally required that e2fsck only be run on the bad device before placing the device back into service.
In the vast majority of cases, the Lustre software can cope with any inconsistencies found on the disk and between other devices in the file system.
For problem analysis, it is strongly recommended that e2fsck be run under a logger, like script, to record all of the output and changes that are made to the file system in case this information is needed later.
If time permits, it is also a good idea to first run e2fsck in non-fixing mode (-n option) to assess the type and extent of damage to the file system. The drawback is that in this mode, e2fsck does not recover the file system journal, so there may appear to be file system corruption when none really exists.
To address concern about whether corruption is real or only due to the journal not being replayed, you can briefly mount and unmount the ldiskfs file system directly on the node with the Lustre file system stopped, using a command similar to:
mount -t ldiskfs /dev/{ostdev} /mnt/ost; umount /mnt/ost
This causes the journal to be recovered.
The e2fsck utility works well when fixing file system corruption (better than similar file system recovery tools and a primary reason why ldiskfs was chosen over other file systems). However, it is often useful to identify the type of damage that has occurred so an ldiskfs expert can make intelligent decisions about what needs fixing, in place ofe2fsck.
root# {stop lustre services for this device, if running}
root# script /tmp/e2fsck.sda
Script started, file is /tmp/e2fsck.sda
root# mount -t ldiskfs /dev/sda /mnt/ost
root# umount /mnt/ost
root# e2fsck -fn /dev/sda # don't fix file system, just check for corruption
:
[e2fsck output]
:
root# e2fsck -fp /dev/sda # fix errors with prudent answers (usually yes)
In cases where an ldiskfs MDT or OST becomes corrupt, you need to run e2fsck to ensure local filesystem consistency, then use LFSCK to run a distributed check on the file system to resolve any inconsistencies between the MDTs and OSTs, or among MDTs.
-
Stop the Lustre file system.
-
Run
e2fsck -fon the individual MDT/OST that had problems to fix any local file system damage.We recommend running
e2fsckunder script, to create a log of changes made to the file system in case it is needed later. Aftere2fsckis run, bring up the file system, if necessary, to reduce the outage window.
The simplest problem to resolve is that of orphaned objects. When the LFSCK layout check is run, these objects are linked to new files and put into .lustre/lost+found/MDT*xxxx* in the Lustre file system (where MDTxxxx is the index of the MDT on which the orphan was found), where they can be examined and saved or deleted as necessary.
Introduced in Lustre 2.7With Lustre version 2.7 and later, LFSCK will identify and process orphan objects found on MDTs as well.
One problem encountered in a Lustre file system environment is when an OST becomes unavailable due to a network partition, OSS node crash, etc. When this happens, the OST's clients pause and wait for the OST to become available again, either on the primary OSS or a failover OSS. When the OST comes back online, the Lustre file system starts a recovery process to enable clients to reconnect to the OST. Lustre servers put a limit on the time they will wait in recovery for clients to reconnect.
During recovery, clients reconnect and replay their requests serially, in the same order they were done originally. Until a client receives a confirmation that a given transaction has been written to stable storage, the client holds on to the transaction, in case it needs to be replayed. Periodically, a progress message prints to the log, stating how_many/expected clients have reconnected. If the recovery is aborted, this log shows how many clients managed to reconnect. When all clients have completed recovery, or if the recovery timeout is reached, the recovery period ends and the OST resumes normal request processing.
If some clients fail to replay their requests during the recovery period, this will not stop the recovery from completing. You may have a situation where the OST recovers, but some clients are not able to participate in recovery (e.g. network problems or client failure), so they are evicted and their requests are not replayed. This would result in any operations on the evicted clients failing, including in-progress writes, which would cause cached writes to be lost. This is a normal outcome; the recovery cannot wait indefinitely, or the file system would be hung any time a client failed. The lost transactions are an unfortunate result of the recovery process.
Note
The failure of client recovery does not indicate or lead to filesystem corruption. This is a normal event that is handled by the MDT and OST, and should not result in any inconsistencies between servers.
Note
The version-based recovery (VBR) feature enables a failed client to be ''skipped'', so remaining clients can replay their requests, resulting in a more successful recovery from a downed OST. For more information about the VBR feature, see Lustre File System Recovery(Version-based Recovery).
LFSCK is an administrative tool for checking and repair of the attributes specific to a mounted Lustre file system. It is similar in concept to an offline fsck repair tool for a local filesystem, but LFSCK is implemented to run as part of the Lustre file system while the file system is mounted and in use. This allows consistency checking and repair of Lustre-specific metadata without unnecessary downtime, and can be run on the largest Lustre file systems with minimal impact to normal operations.
LFSCK can verify and repair the Object Index (OI) table that is used internally to map Lustre File Identifiers (FIDs) to MDT internal ldiskfs inode numbers, in an internal table called the OI Table. An OI Scrub traverses the OI table and makes corrections where necessary. An OI Scrub is required after restoring from a file-level MDT backup ( the section called “ Backing Up and Restoring an MDT or OST (ldiskfs Device Level)”), or in case the OI Table is otherwise corrupted. Later phases of LFSCK will add further checks to the Lustre distributed file system state. LFSCK namespace scanning can verify and repair the directory FID-in-dirent and LinkEA consistency.
Introduced in Lustre 2.6In Lustre software release 2.6, LFSCK layout scanning can verify and repair MDT-OST file layout inconsistencies. File layout inconsistencies between MDT-objects and OST-objects that are checked and corrected include dangling reference, unreferenced OST-objects, mismatched references and multiple references.
Introduced in Lustre 2.7
In Lustre software release 2.7, LFSCK layout scanning is enhanced to support verify and repair inconsistencies between multiple MDTs.
Control and monitoring of LFSCK is through LFSCK and the lctl get_param command. LFSCK supports three types of interface: switch interface, status interface, and adjustment interface. These interfaces are detailed below.
LFSCK can be started after the MDT is mounted using the lctl lfsck_start command.
lctl lfsck_start <-M | --device [MDT,OST]_device> \
[-A | --all] \
[-c | --create_ostobj on | off] \
[-C | --create_mdtobj on | off] \
[-d | --delay_create_ostobj on | off] \
[-e | --error {continue | abort}] \
[-h | --help] \
[-n | --dryrun on | off] \
[-o | --orphan] \
[-r | --reset] \
[-s | --speed ops_per_sec_limit] \
[-t | --type check_type[,check_type...]] \
[-w | --window_size size]
The various lfsck_start options are listed and described below. For a complete list of available options, type lctl lfsck_start -h.
| Option | Description |
|---|---|
| `-M | --device` |
| `-A | --all` |
| `-c | --create_ostobj` |
| `-C | --create_mdtobj` |
| `-d | --delay_create_ostobj` |
| `-e | --error` |
| `-h | --help` |
| `-n | --dryrun` |
| `-o | --orphan` |
| `-r | --reset` |
| `-s | --speed` |
| `-t | --type` |
| `-w | --window_size` |
To stop LFSCK when the MDT is mounted, use the lctl lfsck_stop command.
lctl lfsck_stop <-M | --device [MDT,OST]_device> \
[-A | --all] \
[-h | --help]
The various lfsck_stop options are listed and described below. For a complete list of available options, type lctl lfsck_stop -h.
| Option | Description |
|---|---|
| `-M | --device` |
| `-A | --all` |
| `-h | --help` |
Check the LFSCK global status via a single lctl lfsck_query command on the MDS.
lctl lfsck_query <-M | --device MDT_device> \
[-h | --help] \
[-t | --type lfsck_type[,lfsck_type...]] \
[-w | --wait]
The various lfsck_query options are listed and described below. For a complete list of available options, type lctl lfsck_query -h.
| Option | Description |
|---|---|
| `-M | --device` |
| `-h | --help` |
| `-t | --type` |
| `-w | --wait` |
For each LFSCK component there is a dedicated procfs interface to trace the corresponding LFSCK component status. For OI Scrub, the interface is the OSD layer procfs interface, named oi_scrub. To display OI Scrub status, the standard lctl get_param command is used as shown in the usage below.
lctl get_param -n osd-ldiskfs.FSNAME-[MDT_target|OST_target].oi_scrub
| Information | Detail |
|---|---|
| General Information | - Name: OI_scrub. - OI scrub magic id (an identifier unique to OI scrub). - OI files count. --- Status: one of the status - init, scanning, completed, failed, stopped, paused, orcrashed. - Flags: including - recreated(OI file(s) is/are removed/recreated), inconsistent(restored from file-level backup), auto(triggered by non-UI mechanism), and upgrade(from Lustre software release 1.8 IGIF format.) - Parameters: OI scrub parameters, like failout. - Time Since Last Completed. - Time Since Latest Start. - Time Since Last Checkpoint. - Latest Start Position: the position for the latest scrub started from. - Last Checkpoint Position. - First Failure Position: the position for the first object to be repaired. - Current Position. |
| Statistics | - Checked total number of objects scanned. - Updated total number of objects repaired. - Failed total number of objects that failed to be repaired. - No Scrub total number of objects marked LDISKFS_STATE_LUSTRE_NOSCRUB and skipped. - IGIF total number of objects IGIF scanned. - Prior Updated how many objects have been repaired which are triggered by parallel RPC. - Success Count total number of completed OI_scrub runs on the target. - Run Time how long the scrub has run, tally from the time of scanning from the beginning of the specified MDT target, not include the paused/failure time among checkpoints. - Average Speed calculated by dividing Checked by run_time. - Real-Time Speed the speed since last checkpoint if the OI_scrub is running. - Scanned total number of objects under /lost+found that have been scanned. - Repaired total number of objects under /lost+found that have been recovered. - Failed total number of objects under /lost+found failed to be scanned or failed to be recovered. |
Introduced in Lustre 2.4
The namespace component is responsible for checks described in the section called “ Checking the file system with LFSCK”. The procfs interface for this component is in the MDD layer, named lfsck_namespace. To show the status of this component, lctl get_param should be used as described in the usage below.
The LFSCK namespace status output refers to phase 1 and phase 2. Phase 1 is when the LFSCK main engine, which runs on each MDT, linearly scans its local device, guaranteeing that all local objects are checked. However, there are certain cases in which LFSCK cannot know whether an object is consistent or cannot repair an inconsistency until the phase 1 scanning is completed. During phase 2 of the namespace check, objects with multiple hard-links, objects with remote parents, and other objects which couldn't be verified during phase 1 will be checked.
lctl get_param -n mdd. FSNAME-MDT_target.lfsck_namespace
| Information | Detail |
|---|---|
| General Information | - Name: lfsck_namespace - LFSCK namespace magic. - LFSCK namespace version.. - Status: one of the status - init, scanning-phase1, scanning-phase2, completed, failed,stopped, paused, partial, co-failed, co-stopped or co-paused. - Flags: including - scanned-once(the first cycle scanning has been completed),inconsistent(one or more inconsistent FID-in-dirent or LinkEA entries that have been discovered), upgrade(from Lustre software release 1.8 IGIF format.) - Parameters: including dryrun, all_targets, failout, broadcast, orphan, create_ostobjand create_mdtobj. - Time Since Last Completed. - Time Since Latest Start. - Time Since Last Checkpoint. - Latest Start Position: the position the checking began most recently. - Last Checkpoint Position. - First Failure Position: the position for the first object to be repaired. - Current Position. |
| Statistics | - Checked Phase1 total number of objects scanned during scanning-phase1. - Checked Phase2 total number of objects scanned during scanning-phase2. - Updated Phase1 total number of objects repaired during scanning-phase1. - Updated Phase2 total number of objects repaired during scanning-phase2. - Failed Phase1 total number of objets that failed to be repaired during scanning-phase1. - Failed Phase2 total number of objets that failed to be repaired during scanning-phase2. - directories total number of directories scanned. - multiple_linked_checked total number of multiple-linked objects that have been scanned. - dirent_repaired total number of FID-in-dirent entries that have been repaired. - linkea_repaired total number of linkEA entries that have been repaired. - unknown_inconsistency total number of undefined inconsistencies found in scanning-phase2. - unmatched_pairs_repaired total number of unmatched pairs that have been repaired. - dangling_repaired total number of dangling name entries that have been found/repaired. - multi_referenced_repaired total number of multiple referenced name entries that have been found/repaired. - bad_file_type_repaired total number of name entries with bad file type that have been repaired. - lost_dirent_repaired total number of lost name entries that have been re-inserted. - striped_dirs_scanned total number of striped directories (master) that have been scanned. - striped_dirs_repaired total number of striped directories (master) that have been repaired. - striped_dirs_failed total number of striped directories (master) that have failed to be verified. - striped_dirs_disabled total number of striped directories (master) that have been disabled. - striped_dirs_skipped total number of striped directories (master) that have been skipped (for shards verification) because of lost master LMV EA. - striped_shards_scanned total number of striped directory shards (slave) that have been scanned. - striped_shards_repaired total number of striped directory shards (slave) that have been repaired. - striped_shards_failed total number of striped directory shards (slave) that have failed to be verified. - striped_shards_skipped total number of striped directory shards (slave) that have been skipped (for name hash verification) because LFSCK does not know whether the slave LMV EA is valid or not. - name_hash_repaired total number of name entries under striped directory with bad name hash that have been repaired. - nlinks_repaired total number of objects with nlink fixed. - mul_linked_repaired total number of multiple-linked objects that have been repaired. - local_lost_found_scanned total number of objects under /lost+found that have been scanned. - local_lost_found_moved total number of objects under /lost+found that have been moved to namespace visible directory. - local_lost_found_skipped total number of objects under /lost+found that have been skipped. - local_lost_found_failed total number of objects under /lost+found that have failed to be processed. - Success Count the total number of completed LFSCK runs on the target. - Run Time Phase1 the duration of the LFSCK run during scanning-phase1. Excluding the time spent paused between checkpoints. - Run Time Phase2 the duration of the LFSCK run during scanning-phase2. Excluding the time spent paused between checkpoints. - Average Speed Phase1 calculated by dividing checked_phase1 by run_time_phase1. - Average Speed Phase2 calculated by dividing checked_phase2 by run_time_phase1. - Real-Time Speed Phase1 the speed since the last checkpoint if the LFSCK is runningscanning-phase1. - Real-Time Speed Phase2 the speed since the last checkpoint if the LFSCK is runningscanning-phase2. |
Introduced in Lustre 2.6
The layout component is responsible for checking and repairing MDT-OST inconsistency. The procfs interface for this component is in the MDD layer, named lfsck_layout, and in the OBD layer, named lfsck_layout. To show the status of this component lctl get_param should be used as described in the usage below.
The LFSCK layout status output refers to phase 1 and phase 2. Phase 1 is when the LFSCK main engine, which runs on each MDT/OST, linearly scans its local device, guaranteeing that all local objects are checked. During phase 1 of layout LFSCK, the OST-objects which are not referenced by any MDT-object are recorded in a bitmap. During phase 2 of the layout check, the OST-objects in the bitmap will be re-scanned to check whether they are really orphan objects.
lctl get_param -n mdd.
FSNAME-
MDT_target.lfsck_layout
lctl get_param -n obdfilter.
FSNAME-
OST_target.lfsck_layout
| Information | Detail |
|---|---|
| General Information | - Name: lfsck_layout - LFSCK namespace magic.LFSCK namespace version.. - Status: one of the status - init, scanning-phase1, scanning-phase2, completed, failed,stopped, paused, crashed, partial, co-failed, co-stopped, or co-paused. - Flags: including - scanned-once(the first cycle scanning has been completed),inconsistent(one or more MDT-OST inconsistencies have been discovered),incomplete(some MDT or OST did not participate in the LFSCK or failed to finish the LFSCK) or crashed_lastid(the lastid files on the OST crashed and needs to be rebuilt). - Parameters: including dryrun, all_targets and failout. - Time Since Last Completed. - Time Since Latest Start. - Time Since Last Checkpoint. - Latest Start Position: the position the checking began most recently. - Last Checkpoint Position. - First Failure Position: the position for the first object to be repaired. - Current Position. |
| Statistics | - Success Count: the total number of completed LFSCK runs on the target. - Repaired Dangling: total number of MDT-objects with dangling reference have been repaired in the scanning-phase1. - Repaired Unmatched Pairs total number of unmatched MDT and OST-object pairs have been repaired in the scanning-phase1Repaired Multiple Referenced total number of OST-objects with multiple reference have been repaired in the scanning-phase1. - Repaired Orphan total number of orphan OST-objects have been repaired in the scanning-phase2. - Repaired Inconsistent Owner total number.of OST-objects with incorrect owner information have been repaired in the scanning-phase1. - Repaired Others total number of.other inconsistency repaired in the scanning phases.Skipped Number of skipped objects. - Failed Phase1 total number of objects that failed to be repaired during scanning-phase1. - Failed Phase2 total number of objects that failed to be repaired during scanning-phase2. - Checked Phase1 total number of objects scanned during scanning-phase1. - Checked Phase2 total number of objects scanned during scanning-phase2. - Run Time Phase1 the duration of the LFSCK run during scanning-phase1. Excluding the time spent paused between checkpoints. - Run Time Phase2 the duration of the LFSCK run during scanning-phase2. Excluding the time spent paused between checkpoints. - Average Speed Phase1 calculated by dividing checked_phase1 by run_time_phase1. - Average Speed Phase2 calculated by dividing checked_phase2 by run_time_phase1. - Real-Time Speed Phase1 the speed since the last checkpoint if the LFSCK is runningscanning-phase1. - Real-Time Speed Phase2 the speed since the last checkpoint if the LFSCK is runningscanning-phase2. |
Introduced in Lustre 2.6
The LFSCK upper speed limit can be changed using lctl set_param as shown in the usage below.
lctl set_param mdd.${FSNAME}-${MDT_target}.lfsck_speed_limit=
N
lctl set_param obdfilter.${FSNAME}-${OST_target}.lfsck_speed_limit=
N
| 0 | No speed limit (run at maximum speed.) |
|---|---|
| positive integer | Maximum number of objects to scan per second. |
The auto_scrub parameter controls whether OI scrub will be triggered when an inconsistency is detected during OI lookup. It can be set as described in the usage and values sections below.
There is also a noscrub mount option (see the section called “ mount.lustre”) which can be used to disable automatic OI scrub upon detection of a file-level backup at mount time. If the noscrub mount option is specified,auto_scrub will also be disabled, so OI scrub will not be triggered when an OI inconsistency is detected. Auto scrub can be renabled after the mount using the command shown in the usage. Manually starting LFSCK after mounting provides finer control over the starting conditions.
lctl set_param osd_ldiskfs.${FSNAME}-${MDT_target}.auto_scrub=N
where N is an integer as described below.
Introduced in Lustre 2.5
Note
Lustre software 2.5 and later supports -P option that makes the set_param permanent.
| 0 | Do not start OI Scrub automatically. |
|---|---|
| positive integer | Automatically start OI Scrub if inconsistency is detected during OI lookup. |