From: Markus Mikkolainen <itm@kabuto.fi>
To: LVM general discussion and development <linux-lvm@redhat.com>
Cc: mark@xwax.org
Subject: Re: [linux-lvm] corruption on reattaching cache
Date: Fri, 10 Jun 2016 13:51:26 +0300 (EEST) [thread overview]
Message-ID: <alpine.LRH.2.02.1606101349530.5953@inet.itmo.dyndns.org> (raw)
In-Reply-To: <f8db9f60-3250-1a34-4517-1bf9fe43f700@redhat.com>
could there atleast be some kind of a warning if the reattaching will
result in you destroying your filesystem? or possibly make the
"--splitcache" warn that this is a debug feature and the result might be
bad?
basically NOTHING suggested to me that i might be doing something that
could destroy my filesystem.
> Dne 9.6.2016 v 22:24 Markus Mikkolainen napsal(a):
>> I seem to have hit the same snag as Mark describes in his post.
>>
>> https://www.redhat.com/archives/linux-lvm/2015-April/msg00025.html
>>
>> with kernel 4.4.6 I detached (--splitcache) a writeback cache from a
>> mounted
>> lv which was then synchronized and detached. Then I reattached it and
>> shortly
>> detached it again. What was interesting is that after the second detach it
>> synchronized AGAIN starting from 100% , and then I started getting
>> filesystem
>> errors. I immediately shutdown, and forced an fsck , and didnt lose that
>> much
>> data, but still had some stuff to correct.
>>
>> It looked to me like a detached cache, being reattached will retain all
>> cached
>> data on it, even though it was supposed to be written to the backing disk,
>> and
>> then instead of marking it clean on attaching, it will continue serving
>> old
>> data from the cache.
>>
>
>
> Yes - known issue, --splitcache is rather for 'debugging' purposes.
> Use --uncache and create new cache when needed.
>
> Splitted cache needs to be cleared on reattachment - but that needs further
> code rework.
>
> The idea behind is - we want to support 'offline' writeback of data as ATM
> cache target doesn't work well if there is any disk error - i.e. cache is in
> writeback mode and has 'error' sector - you can't clean such cache...
>
> Regards
>
> Zdenek
>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>
>
next prev parent reply other threads:[~2016-06-10 10:51 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-09 20:24 [linux-lvm] corruption on reattaching cache Markus Mikkolainen
2016-06-10 9:09 ` Zdenek Kabelac
2016-06-10 10:51 ` Markus Mikkolainen [this message]
2016-06-13 8:48 ` Zdenek Kabelac
2016-06-11 9:24 ` Mark Hills
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