Gary Stainburn wrote:
> 1) I intended to use striping (raid 5?) over the six disks.
Striping without fault tolerance is RAID0. [1]
> Am I right in thinking that this improves performance by spreading the workload more
>evenly
> over the disks?
Yes, over many channels and drives.
> If one of the drives fails, I understand the system will
> carry on but generate warnings.
No, not possible under RAID0. You're thinking of RAID1. [1]
> 2) If I use mirroring (raid 0?) for /usr
RAID1 [1]
> 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?
Not to my knowledge. From a software standpoint, it's only one drive. If it
fails, it fails. It doesn't know to go to the next disk and try again. And since
you're talking about /usr being on it, it won't even know that the disk is a RAID
device unless it can get to it.
> 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?
Striping doesn't need same geometry, however mirroring does. And I've never tried
to "break" a disk into multiple partitions and stripe/mirror partitions. I've always
did the whole drive.
> 4) Can anyone suggest better alternatives?
That all depends on what you really want to achieve. In my opinion, you can take
the first 2 drives and mirror them, then take the next 4 and stripe them, giving you a
9GB with fault tolerance and a 36GB without fault tolerance system. Presumably you'll
be putting / on the 9GB and something like /home on the 36GB. Not sure why you'd need
/usr to be on a different system. /usr itself doesn't exactly grow much after
installation, however things like /usr/local do, so you can drop that elsewhere. For
example:
/ -> 9GB
/usr/local -> 10GB partition on 36GB striped RAID
/home -> 26GB partition on 36GB striped RAID
This leaves the rest of /usr on the main 9GB drive.
> 5) Can anyone suggest some good (read simple) Raid documentation I could read?
[1] General RAID* information: http://www.acnc.com/04_01_00.html
There's also a RAID-HOWTO for Linux. Check the HOWTO pages.
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