On Thu, Jan 24, 2002 at 03:22:18PM +0000, Gary Stainburn wrote:
> I seem to remember a thread a while back about there being a problem with
> putting /usr on a raid device as /usr is needed to provide raid and there
> creates a catch-22 situation.
I ran into this, but when I installed from scratch and had the installer
create the software RAID partitions (I was using mirroring) it worked fine.
The latest raidtools includes a fix for this a swell.
> This surely creates a single-point-of-failure which reduces the effect of
> raid. My questions therefore are:
>
> 1) I intended to use striping (raid 5?) over the six disks. Am I right in
> thinking that this improves performance by spreading the workload more evenly
> over the disks? If one of the drives fails, I understand the system will
> carry on but generate warnings. Is the S/w raid in Linux good enough to let
> me swap out and rebuild the disk without loss of service?
No! Striping is not RAID-5. Striping offers NO redundancy - if any member
fails, you've lost *all* the data on *all* members.
RAID-5 does offer the redundancy and should allow you to continue running.
> 2) If I use mirroring (raid 0?) for /usr, could it boot up using one of the
> mirrors without the raid s/w and then once /usr and raid is available then
> turn on the mirroring? If the 1st mirror then failed, could I carry on using
> the second mirror without system loss and be able to swap out and rebuild the
> faulty disk?
Read the raid documentation. You basically set up /usr with a single member.
The raid software is running, but you've got a "failed" member - ie, the missing
member. You can then later add the member in.
> 3) Can I mix raid devices on the same physical devices. For example can I
> mirror 4GB of the 1st two disks and stripe everything else? If the disks
> used for striping all need to be the same geometry then presumably this won't
> work. Could I then mirror the first two disks and stripe the other 4?
All the software raid tools work on a partition by partition basis. You should
read the Linux software-RAID howto - a quick google search will find it for you.
.../Ed
--
Ed Wilts, Mounds View, MN, USA
mailto:[EMAIL PROTECTED]
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