Questions about RAID

Hi All,

I’m planning a RAID 5 setup for a new server and, after reading everything I could find, have some questions.

  1. I understand that I should be able to boot from a RAID 1 array. Is it possible to boot from a RAID 5 array? It seems the boot process would be the same but no mention is made of being able to do this.

  2. I read one FAQ/HOWTO that indicated that to hot-swap drives in a Linux software RAID could cause severe hardware and/or data damage and ruin your day. In another place they explain how to perform a hot-swap and make no mention of any danger. What’s the story? Is it safe?

  3. If I cannot boot from a RAID 5 array, is it possible to have a RAID 1 array as a boot device and also have a RAID 5 array for data storage on the same computer?

  4. I’d like to have mdadm monitor my arrays and send an email to notify of a failure. If I have to run multiple arrays (1 & 5) on the same computer, can mdadm monitor both arrays simultaneously?

Sorry for all the questions but I want to make sure I’m not screwing myself before I order hardware.

Thanks for any and all advise,
Steve

1 Not from a software RAID5. The BIOS doesn’t know how to form the array so will not be able to boot off it. However hardware RAID5 is integral from power up so the BIOS will be able to boot off it.

2, Dunno.

  1. Yes.

  2. Yes.

> 1. I understand that I should be able to boot from a RAID 1 array. Is
> it possible to boot from a RAID 5 array? It seems the boot process
> would be the same but no mention is made of being able to do this.
I have a server running RHEL that boots via RAID 5. In the past I believe it
was not doable, but now is not an issue.

> 2. I read one FAQ/HOWTO that indicated that to hot-swap drives in a
> Linux software RAID could cause severe hardware and/or data damage and
> ruin your day. In another place they explain how to perform a hot-swap
> and make no mention of any danger. What’s the story? Is it safe?
Probably depends on the RAID controller, management software and version of
LInux. A lot can go wrong. I have not had to do this fortunately. I have
replaced mirrors before but I shut the box down to do so. Adaptec has
their Storage Manager product which runs under Linux and allows you to mark
drives for replacement so I assume it could handle a hot swap. YMMV.

> 3. If I cannot boot from a RAID 5 array, is it possible to have a RAID
> 1 array as a boot device and also have a RAID 5 array for data storage
> on the same computer?
Yes.

> 4. I’d like to have mdadm monitor my arrays and send an email to notify
> of a failure. If I have to run multiple arrays (1 & 5) on the same
> computer, can mdadm monitor both arrays simultaneously?
I wouldn’t see why not, just pass to mdadm the device your interested in
monitoring.

Yes, I have a RHEL server with RAID5 too, but it’s hardware RAID5.