From: Mike Snitzer <msnitzer@lnxi.com>
To: linux-hotplug@vger.kernel.org
Subject: Re: raiddetect support for Linux software RAID?
Date: Tue, 04 May 2004 20:42:23 +0000 [thread overview]
Message-ID: <20040504144223.A14126@lnxi.com> (raw)
In-Reply-To: <4093C82C.6030306@backtobasicsmgmt.com>
On Sat, May 01 2004 at 09:54,
Kevin P. Fleming <kpfleming@backtobasicsmgmt.com> wrote:
> I'm wondering if anyone has planned on putting Linux software RAID (md)
> detection into the raiddetect tool. Currently I use mdadm to scan all
> devices to look for my RAID(s), but it's got some problems:
>
> - it's not hotplug driven, it has to be run over all devices
> - it's noisy because it wants to scan everything in /dev
> - i can't see what's there without trying to activate it
>
> raiddetect would be a nice addition, I would be able to tell that a
> complete array has appeared and just use mdadm to start it up. Thoughts?
The notion of a "complete array" is somewhat difficult to define in terms
of hotplug. Traditionally a raid array is intialized _after_ all block
devices have been detected and made available. The piece-wise
availability of hotplug detected block devices makes it hard to know when
its safe/right to initialize the raid array.
E.g. raid initialization special case: What if a raid array spans two
disk controllers; and the first controller happens to have enough disks
for the array to opperate in degraded mode? Once the other controller
makes its disks available the raid could already be online and the disks
that got left behind would need to re-sync. This is a problem common to
all software raid and hotplug; regardless of whether your using Linux's MD
or DM (EVMS).
If anyone has great ideas on ways to implement a barrier for the raid
initialization special case (and any others I may be overlooking) let me
know.
Mike
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next prev parent reply other threads:[~2004-05-04 20:42 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-05-01 15:54 raiddetect support for Linux software RAID? Kevin P. Fleming
2004-05-04 20:42 ` Mike Snitzer [this message]
2004-05-05 0:34 ` Kevin P. Fleming
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