From: Sebastian Riemer <sebastian.riemer@profitbricks.com>
To: NeilBrown <neilb@suse.de>
Cc: Neil Matai <neil@matai.kiwi.nz>, linux-raid@vger.kernel.org
Subject: Re: Simultaneous assembly on multiple hosts
Date: Mon, 06 May 2013 11:05:34 +0200 [thread overview]
Message-ID: <5187725E.5050803@profitbricks.com> (raw)
In-Reply-To: <20130506163203.7a65786b@notabene.brown>
On 06.05.2013 08:32, NeilBrown wrote:
> On Sat, 4 May 2013 14:01:46 +1200 Neil Matai <neil@matai.kiwi.nz>
> wrote:
>
>> Hi all,
>>
>> Is it dangerous have an array assembled on two hosts at the same
>> time? Say I have servers A and B exporting devices a and b via
>> ATA over Ethernet or similar to hosts C and D. If a and b are
>> components of an array then both C and D automatically assemble
>> the array as soon as the components a and b are exported but is
>> this safe (on the proviso that only one of C or D is ever writing
>> to the array at any time and that there is no write-behind
>> caching above the array device)?
>>
>
> Yes, it is dangerous. Both hosts will try to update the metadata
> and will trip over each other.
This is why we've implemented automatic super block + bitmap reload
upon first IO. Before, the MD device acts as a read-only device with
read-only super block. This is rather complex to make it safe.
This is also difficult to merge with mainline behavior.
Get yourself a kernel developer. ;-)
Cheers,
Sebastian
prev parent reply other threads:[~2013-05-06 9:05 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-04 2:01 Simultaneous assembly on multiple hosts Neil Matai
[not found] ` <CALFpzo6CUZSeAcNK1A=8HdyjaGnKiN4Mtt01u_w=3p7WG-wY2A@mail.gmail.com>
2013-05-04 3:22 ` Neil Matai
2013-05-06 6:32 ` NeilBrown
2013-05-06 9:05 ` Sebastian Riemer [this message]
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