RAID5 + 1 extra disk HOW
roland at cat.be
Sun Oct 12 09:21:01 UTC 2008
On Sat, 11 Oct 2008 23:56:34 +0200, Bill Davidsen <davidsen at tmr.com> wrote:
> roland wrote:
>> I have a server running on RAID5, on which I would like to add a 4th
>> disk, with a seperated filesystem. I need to have some workspace. The
>> same disk could be used to replace a failing disk.
> This is a spare disk, and can be used only as such. I'm not sure what
> you had in mind by "seperated filesystem," but you can't install another
> drive such that Linux will use the drive in two ways at once. If that
> was your intent it pretty much isn't going to work, and if the spare was
> deployed all data on it would be lost.
>> Stuart Sears explaned me howto install this disk as a hot spare, but it
>> looks to me a little bit to dangereous. This server is serving 20
>> workstations, so I need to do this without taking to many risks. I
>> admit to be a novice on the matter of diskmanagement. I always do
>> standard installation of a filesystem.
> Assuming you just want to add a spare, something like this works fine:
> mdadm --add /dev/md0 /dev/sdf1
> Then a cat of /proc/mdstat should show the device added, running as a
> spare. I did that, then failed one of the existing drives, and the array
> rebuilt on the spare just fine, and I got a message from monitor mode
> saying it happened and was fixed.
I have to mention that the raid5 was build with the IBM utilities on this
server x3500. So I suppose this mdadm wouldn't work. Or am I wrong?
Secondly, I need extra space only as a workarea.
That's why I thought, maybe I can:
- insert a 4th disk and add a filesystem, that isn't part of the raid5.
- insert a 4th and 5th disk and configure it as a raid1, to be used for
non critical applications
In case of failure of the raid5, I could could use the 4th disk to replace
the failing disk of the raid5 and let the ibm utilities rebuild the raid5
Does this makes sense?
>> So if someone could tell me howto do this in a simple way. I searched
>> the internet for a simple howto, but was unsuccessful. I have to do
>> this at a client in France, few hours driving
>> Could someone keep me from having a sleepless night?
> I would test the existing array before counting on it to be okay, just
> in case a bad spot developed.See the wiki (http://linux-raid.osdl.org).
> Oh, and there is a linux-raid mailing list where there are lots of us
> who have found problems the hard way and want to share.
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