Data corruption, md5 changes on every mount
Hi guys,
I have a 2TiB XFS which is about 60% full. Recently I've noticed that the daily inc. backup reports file contents change for files that are not supposed to change.
I've created an LVM snapshot and ran xfs_check/xfs_repair. xfs_check did report a few problems (unknown node type). After that I ran a simple test: mount, calculate md5 of the problematic files, report if it changed, umount, sleep 10 sec. That script reported that md5 sum of at least one file was changing on every cycle.
Analyzing the differences I found that a 4k block that should contain all zeros sometimes contains random garbage (luckily most of the files are pcm wavs, so it's easy to verify). However I did not analyze every occurrence so this may be not 100% true. The files do not look as they are sparse according to du. Interestingly one of them appears to occupy one block more than necessary.
Then I did cp -a file newfile, mv newfile file and re-ran the test. No problems reported since.
As there were a few unclean umounts I think most likely it is a filesystem corruption that went unspotted by xfs_repair. It would not surprise me too much because xfs_repair took just 3.5 min.
Any ideas? I could just copy the files and pretend noting happened but is there a guarantee that doing so won't corrupt other data?
Best regards,
Signature · 6 lines
Dmitry Panov _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Quoted 5 lines · Dmitry Panov
Hi guys,
I have a 2TiB XFS which is about 60% full. Recently I've noticed that the daily inc. backup reports file contents change for files that are not supposed to change.
What kernel/platform? What version of xfsprogs? What kind of storage?
Quoted 5 lines
I've created an LVM snapshot and ran xfs_check/xfs_repair.
xfs_checkdid report a few problems (unknown node type). After that I ran a simple test: mount, calculate md5 of the problematic files, report if it changed, umount, sleep 10 sec. That script reported that md5 sum of at least one file was changing on every cycle.
That sounds like you've got a dodgy drive.
Quoted 6 lines
Analyzing the differences I found that a 4k block that should contain all zeros sometimes contains random garbage (luckily most of the files are pcm wavs, so it's easy to verify). However I did not analyze every occurrence so this may be not 100% true. The files do not look as they are sparse according to du. Interestingly one of them appears to occupy one block more than necessary.
XFS can allocate blocks beyond EOF - it's completely valid to do so.
Quoted 2 lines
Then I did cp -a file newfile, mv newfile file and re-ran the test. No problems reported since.
So the file is now in a different physical location on disk. Defintely sounds like a dodgy disk to me.
Quoted 3 lines
As there were a few unclean umounts I think most likely it is a filesystem corruption that went unspotted by
xfs_repair. It would not surprise me too much becausexfs_repairtook just 3.5 min.
The run time of xfs_repair is determined by how much IO it needs to do to read all the metadata. Your filesystem is not all that densely populated with metadata, so it doesn't take very long to run. The short runtime does not mean it hasn't checked you filesystem properly.
Think about scale or a minute - take your filesystem and scale it linearly in all dimensions - a repair rate of 1.5m per TB means 2.5hrs for a 100TB filesystem or a day for a PB sized filesystem. The speed you are seeing doesn't seem quite so fast now, does it?
Quoted 2 lines
Any ideas? I could just copy the files and pretend noting happened but is there a guarantee that doing so won't corrupt other data?
I'd start by replacing hardware....
Cheers,
Dave.
Signature · 7 lines
Dave Chinner [email protected] _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Hi Dave,
Quoted 8 lines · Dave Chinner
Quoted 5 lines · Dmitry Panov
Hi guys,
I have a 2TiB XFS which is about 60% full. Recently I've noticed that the daily inc. backup reports file contents change for files that are not supposed to change.
What kernel/platform? What version of xfsprogs? What kind of storage?
It's linux kernel 3.0.0 at the moment, however it used to run different versions and I can't tell for sure when the problem started. xfsprogs version is 3.1.2.
The storage is a 2 node cluster with hardware RAID1+0 and drbd.
Quoted 6 lines
Quoted 5 lines
I've created an LVM snapshot and ran xfs_check/xfs_repair.
xfs_checkdid report a few problems (unknown node type). After that I ran a simple test: mount, calculate md5 of the problematic files, report if it changed, umount, sleep 10 sec. That script reported that md5 sum of at least one file was changing on every cycle.That sounds like you've got a dodgy drive.
That would be my guess too, however the problem occurs on both nodes (i.e. it doesn't go away when the other node becomes active) and the same files affected which makes hard drives or RAID controller or RAM failure very unlikely.
Is there any way to perform a more thorough check, than xfs_check does?
Best regards,
Signature · 6 lines
Dmitry Panov _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Quoted 9 lines · Dmitry Panov
Hi Dave,
Quoted 6 lines · Dave Chinner
Quoted 5 lines · Dmitry Panov
Hi guys,
I have a 2TiB XFS which is about 60% full. Recently I've noticed that the daily inc. backup reports file contents change for files that are not supposed to change.
Quoted 7 lines
Quoted 2 lines
What kernel/platform? What version of xfsprogs? What kind of storage?
It's linux kernel 3.0.0 at the moment, however it used to run different versions and I can't tell for sure when the problem started. xfsprogs version is 3.1.2.
The storage is a 2 node cluster with hardware RAID1+0 and drbd.
Hmmmm. HA, remote replication, network paths in the storage stack. Not a particularly common setup, so I'd be looking at validating your drbd setup before looking at XFS.....
Quoted 11 lines
Quoted 6 lines
Quoted 5 lines
I've created an LVM snapshot and ran xfs_check/xfs_repair.
xfs_checkdid report a few problems (unknown node type). After that I ran a simple test: mount, calculate md5 of the problematic files, report if it changed, umount, sleep 10 sec. That script reported that md5 sum of at least one file was changing on every cycle.That sounds like you've got a dodgy drive.
That would be my guess too, however the problem occurs on both nodes (i.e. it doesn't go away when the other node becomes active) and the same files affected which makes hard drives or RAID controller or RAM failure very unlikely.
Which simply means the corruption has been replicated.
Given that drbd is in the picture and that has a history of causing filesystem and/or data corruptions, I'd suggest you validate that drbd is not causing problems first. If you can reproduce the data corruption on a storage stack that doesn't have drbd in it, then it's probably a filesystem problem. However, you need to rule out the lower storage layers as the cause first. i.e. once you've validated that your block device is good, then we can start to look at whether the filesystem is the cause.
In general, you need a reliable reproducer to do this, so if you can reproduce the problem anymore, there's little that can be done about it...
Quoted 1 line
Is there any way to perform a more thorough check, than
xfs_checkdoes?
xfs_repair -n is more thorough than xfs_check. But remember, both xfs_check and xfs_repair are only chekcing the filesystem structure, not the contents of your files. The contents of your files are yours to check....
Cheers,
Dave.
Signature · 7 lines
Dave Chinner [email protected] _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Hi Dave,
I've found xfs_bmap and did a few experiments with dd. It looks to me as though it's RAID1 sync problem -- I've got 2 different versions of the data during continuous reads from the device with cache drops inbetween.
So, although the cause of the problem is still unclear, it's definitely not XFS. Thanks for the hint!
Quoted 50 lines · Dave Chinner
Quoted 5 lines · Dmitry Panov
Hi guys,
I have a 2TiB XFS which is about 60% full. Recently I've noticed that the daily inc. backup reports file contents change for files that are not supposed to change.
What kernel/platform? What version of xfsprogs? What kind of storage?
Quoted 5 lines
I've created an LVM snapshot and ran xfs_check/xfs_repair.
xfs_checkdid report a few problems (unknown node type). After that I ran a simple test: mount, calculate md5 of the problematic files, report if it changed, umount, sleep 10 sec. That script reported that md5 sum of at least one file was changing on every cycle.That sounds like you've got a dodgy drive.
Quoted 6 lines
Analyzing the differences I found that a 4k block that should contain all zeros sometimes contains random garbage (luckily most of the files are pcm wavs, so it's easy to verify). However I did not analyze every occurrence so this may be not 100% true. The files do not look as they are sparse according to du. Interestingly one of them appears to occupy one block more than necessary.
XFS can allocate blocks beyond EOF - it's completely valid to do so.
Quoted 2 lines
Then I did cp -a file newfile, mv newfile file and re-ran the test. No problems reported since.
So the file is now in a different physical location on disk. Defintely sounds like a dodgy disk to me.
Quoted 3 lines
As there were a few unclean umounts I think most likely it is a filesystem corruption that went unspotted by
xfs_repair. It would not surprise me too much becausexfs_repairtook just 3.5 min.The run time of
xfs_repairis determined by how much IO it needs to do to read all the metadata. Your filesystem is not all that densely populated with metadata, so it doesn't take very long to run. The short runtime does not mean it hasn't checked you filesystem properly.Think about scale or a minute - take your filesystem and scale it linearly in all dimensions - a repair rate of 1.5m per TB means 2.5hrs for a 100TB filesystem or a day for a PB sized filesystem. The speed you are seeing doesn't seem quite so fast now, does it?
Quoted 2 lines
Any ideas? I could just copy the files and pretend noting happened but is there a guarantee that doing so won't corrupt other data?
I'd start by replacing hardware....
Cheers,
Dave.
Signature · 6 lines
Dmitry Panov _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs