From: Brad Campbell <brad@wasp.net.au>
To: mingz@ele.uri.edu
Cc: linux-raid@vger.kernel.org
Subject: Re: consistency detect
Date: Mon, 11 Oct 2004 12:54:01 +0400 [thread overview]
Message-ID: <416A4A29.9080906@wasp.net.au> (raw)
In-Reply-To: <1097465522.3111.24.camel@localhost.localdomain>
Ming Zhang wrote:
> I have a question on RAID error detect. hope somebody can help me to
> find it out. thanks.
>
> take raid1 as an example, if one disk fail, raid 1 can detect the data
> on disk is compromised and then reconstruct it using a spare disk. this
> is straight forward.
>
> but if one request comes to raid1 and raid1 sends requests to both
> disks, at this time, system reboots because power outage, system
> crashes, or any other reason. then after system reboots, how raid 1
> detects which disk has consistent data? since before reboot, anything
> can happen, data may in disk1 but not in disk2, or in disk2 but not in
> disk1, or not in both disks, or already on both disks.
>
> how raid1 or other raid code deal with this?
In short, it does not deal with it at all. RAID will deal with a disk failure, it has no guarantees
about consistency on power failures, hard lockups or other catastrophic events.
A UPS is cheap insurance against consistency issues in combination with a journalling filesystem.
Brad
next prev parent reply other threads:[~2004-10-11 8:54 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-10-11 3:32 consistency detect Ming Zhang
2004-10-11 8:54 ` Brad Campbell [this message]
2004-10-11 10:42 ` Michael Tokarev
2004-10-11 10:58 ` Brad Campbell
2004-10-11 21:15 ` Ming Zhang
2004-10-11 23:23 ` Neil Brown
2004-10-12 0:05 ` Ming Zhang
2004-10-12 0:13 ` Neil Brown
2004-10-12 0:43 ` Ming Zhang
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