Re: Is there a way to flag specific directories "nodatacow"?

[George Mitchell <george@chinilu.com>]

On 06/02/2013 07:58 PM, Liu Bo wrote:
> On Sun, Jun 02, 2013 at 07:11:10PM -0700, George Mitchell wrote:
>> On 06/02/2013 06:28 PM, Liu Bo wrote:
>>> On Sun, Jun 02, 2013 at 07:40:52AM -0700, George Mitchell wrote:
>>>> I am seeing massive journal corruptions that seem to be unique to
>>>> btrfs and I am suspecting that cow might be causing them.  My
>>>> bandaid fix for this will be to mark the /var filesystem "nodatacow"
>>>> at boot.  But I am wondering if their is any way to flag a
>>>> particular directory as "nodatacow" outside of the mount process.  I
>>>> would like to be able to mark /var/log/journal as "nodatacow" for
>>>> example, without having to declare it a subvolume and mount it
>>>> separately.
>>> Hi George,
>>>
>>> We actually have per-file/directory nodatacow :)
>>>
>>> But please note if you set nodatacow on the particular directory, only
>>> new-created or zero-size files in the directory can follow the nocow rule.
>>>
>>> 'chattr' in the latest e2fsprogs can fit your requirements,
>>> # chattr +C /var/log/journal
>>>
>>> Also, what kind of massive journal corruptions?  Does it look like a
>>> btrfs specific bug?
>>>
>>> thanks,
>>> liubo
>>>
>>>
>> Thanks Liu,
>>
>> That helps a lot! I am very familiar with chattr/lsattr from my ext3
>> days, but didn't know where to look for btrfs options. From what you
>> are telling me the nodatacow option is identical to nodatacow option
>> for ext3. Do the other ext3 options work for btrfs also?
> Besides nodatacow, compression is also supported as per file/directory
> basis.
>
>> As for as the corruption issue, I actually don't know whether the
>> corruptions are real or whether they are being caused by the way the
>> `journalctl --verify` command is interfacing with the filesystem. My
>> suspicion is that metadata fragmentation *might* be somehow messing
>> with the `journalctl --verify` since I can use simply `journalctl`
>> and all the data flows out without error. I just cleaned out the
>> /var/log/journal directory and started fresh and in no time I am
>> seeing corruptions according to `journalctl --verify`. Here is what
>> the output looks like:
> That's weird, AFAIK it shouldn't be.
>
> Does 'dmesg' also complain when these corruptions from 'journalctl --verify'
> occurs?  (well, I'm expecting some csum errors, maybe...)
>
>> ==============================================================================
>>
>> [root@localhost aide]# journalctl --verify
>> Invalid object contents at 130624░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000628-0004de2c1807989c.journal:130624
>> (of 131072, 99%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000628-0004de2c1807989c.journal
>> (Bad message)
>> PASS: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/user-501@e1447322cf904d028439c2d3f17d032e-000000000000065a-0004de2c18d6d96d.journal
>> Invalid object contents at 125264░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-000000000000069a-0004de2c5e323847.journal:125264
>> (of 131072, 95%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-000000000000069a-0004de2c5e323847.journal
>> (Bad message)
>> PASS: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/user-501@e1447322cf904d028439c2d3f17d032e-00000000000006a8-0004de2c73b5f19d.journal
>> Invalid object contents at 128408░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000709-0004de2cedab583c.journal:128408
>> (of 131072, 97%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000709-0004de2cedab583c.journal
>> (Bad message)
>> Invalid object contents at 126736░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-000000000000077f-0004de2d20abe261.journal:126736
>> (of 131072, 96%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-000000000000077f-0004de2d20abe261.journal
>> (Bad message)
>> Invalid object contents at 129600░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-00000000000007ec-0004de2d7c50c186.journal:129600
>> (of 131072, 98%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-00000000000007ec-0004de2d7c50c186.journal
>> (Bad message)
>> PASS: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/user-501@e1447322cf904d028439c2d3f17d032e-00000000000007f1-0004de2d87392b08.journal
>> Invalid object contents at 129256░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000862-0004de2e9a6decf4.journal:129256
>> (of 131072, 98%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000862-0004de2e9a6decf4.journal
>> (Bad message)
>> PASS: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/user-501@e1447322cf904d028439c2d3f17d032e-000000000000087d-0004de2eaee97998.journal
>> Invalid object contents at 126032░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-00000000000008de-0004de2fb88c29cb.journal:126032
>> (of 131072, 96%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-00000000000008de-0004de2fb88c29cb.journal
>> (Bad message)
>> PASS: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/user-501@e1447322cf904d028439c2d3f17d032e-0000000000000947-0004de30cc6f8833.journal
>> Invalid object contents at 130952░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000957-0004de30d6aad93f.journal:130952
>> (of 131072, 99%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000957-0004de30d6aad93f.journal
>> (Bad message)
>> PASS: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/user-501@e1447322cf904d028439c2d3f17d032e-000000000000098b-0004de31213bbbae.journal
>> Invalid object contents at 124168░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-00000000000009d1-0004de31f4c7533d.journal:124168
>> (of 131072, 94%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-00000000000009d1-0004de31f4c7533d.journal
>> (Bad message)
>> Invalid object contents at 130784░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000a47-0004de3312e5e75d.journal:130784
>> (of 131072, 99%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000a47-0004de3312e5e75d.journal
>> (Bad message)
>> PASS: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/user-501@e1447322cf904d028439c2d3f17d032e-0000000000000a8d-0004de33b65f55f2.journal
>> Invalid object contents at 129744░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000abb-0004de33e97b96d8.journal:129744
>> (of 131072, 98%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000abb-0004de33e97b96d8.journal
>> (Bad message)
>> PASS: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/user-501@e1447322cf904d028439c2d3f17d032e-0000000000000ad1-0004de341fd95f50.journal
>> Invalid object contents at 129864░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
>> 0%
>> File corruption detected at /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000b37-0004de34e40af053.journal:129864
>> (of 131072, 99%).
>> FAIL: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system@e1447322cf904d028439c2d3f17d032e-0000000000000b37-0004de34e40af053.journal
>> (Bad message)
>> PASS: /var/log/journal/8846d97f611b49aa9f3d48eeac6a81f2/system.journal
>>
>> ==============================================================================
>>
>> So I want to try forcing "nodatacow" on this directory and see what
>> happens. If that doesn't work, I suppose the next step will be to
>> place this one directory on an ext4 filesystem and mount it
>> externally to the btrfs /var/log. What I do know is that I have a
>> parallel maintenance system on the same hardware using ext4 and it
>> has never had a problem like this. I have also had a boot problem
>> from the beginning and that seems like it got fixed by doing
>> rigorous defragmentation on the btrfs root filesystem. So I really
>> don't know at this point what is causing this problem, but I am
>> determined to do my best to find out. The system I am having the
>> problem with has been running Mageia 3 100% on btrfs RAID 1 migrated
>> from Mageia 2 100% on 3ware hardware RAID 1. Making this transition
>> has been a quite an experience, but the system is up and running
>> fine. This is my day to day production system and since btrfs is
>> where it is right now, this system is rigorously backed up every
>> three hours to a JFS formatted drive and daily to a 4TB btrfs
>> formatted drive. The system is also on UPS, but has actually hard
>> crashed multiple times early on without any resulting data
>> corruption. But only by using btrfs on a production system can I
>> shag out all of these peripheral issues. So thanks so much for the
>> tip, it will get me one step further along in sorting this out.
> Thanks for trying that.
>
> thanks,
> liubo
>
>
Well, nodatacow doesn't fix the problem, so next step which I will try 
to set up tonight, will be to move the journal logging to a separate 
ext4 partition and see if THAT fixes the problem.  If it does, that will 
pretty much implicates btrfs.  If it doesn't, then the problem becomes 
more complex.  What I am really wondering here is what sort of perhaps 
low level stuff the journal verify process might be doing aside from 
just reading the files as data.  If the journal verify process is not 
expecting to encounter a btrfs partition, strange things might happen if 
its attempting any exotic stuff with the files in question.  Other than 
that, of course, I suppose there could be potential timing issues going 
on.  But it is really strange that this problem is occurring on the same 
hardware with btrfs but not with ext4.