From: Phillip Susi <psusi@cfl.rr.com>
To: Petr Rockai <prockai@redhat.com>
Cc: LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] LVM mirror questions
Date: Wed, 6 Oct 2010 14:57:52 -0400 [thread overview]
Message-ID: <4CACC6B0.2030603@cfl.rr.com> (raw)
In-Reply-To: <87ocb7jk3d.fsf@twilight.int.mornfall.net.>
On 10/6/2010 1:40 PM, Petr Rockai wrote:
> Yes, (write) performance is a concern. Otherwise, what you describe is
> perfectly valid and achievable with LVM.
It is? What happens when the log device fails?
>> I don't know how LVM handles issues of PVs that are not permanently dead
>> and come back on line again later. The md driver uses a generation count in
>> the super block to determine which is newer. (How is that updated without loss
>> of efficiency?)
>
> LVM has a generation counter as well. It's only updated on metadata
> writes though, so it doesn't cost anything. (Log is not part of metadata
> in this sense.) When you lose a leg (and use dmeventd), the metadata on
> the remaining PVs is updated to say that. The leg is also yanked from
> the mirror. You can add it as a fresh image (with full resync) if it
> ever comes back.
Why a full resync? With mdadm, it just keeps flagging the dirty chunks
so it only has to copy those when the other disk returns.
next prev parent reply other threads:[~2010-10-06 18:57 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-04 23:55 [linux-lvm] LVM mirror questions Jay
2010-10-05 8:02 ` Petr Rockai
2010-10-06 15:50 ` Jay
2010-10-06 16:37 ` Ray Morris
2010-10-06 17:23 ` Petr Rockai
2010-10-05 15:40 ` Phillip Susi
2010-10-06 15:26 ` Jay
2010-10-06 17:03 ` Stuart D. Gathman
2010-10-06 17:40 ` Petr Rockai
2010-10-06 18:57 ` Phillip Susi [this message]
2010-10-07 12:14 ` Petr Rockai
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