[opensuse] Re: RAID-1 speed -- RAID 1 for? Backup?

Linda Walsh skrev:
Anders Norrbring wrote:
I'm wondering about the speed of a software RAID-1...
If I use one very fast disk, and one pretty much slower, will the volume's
speed be the faster or the slower? If using an ordinary hardware RAID most
controllers gives the volume the highest speed possible, and then mirror in
the background to the slower disk, but is the same true for a software RAID?

Anders.
---
Most likely NO FASTER than the slowest -- it might
be slower due to them being out of sync with each other on writes.

You really don't want to use mismatched drives for a RAID. Use your
faster one as a primary and use the 2nd one as a backup disk -- if you use
xfs on drive 1, you can use xfs_dump to dump all extended file attributes
and access lists, as well as telling it what files or directories not to include with the +d file_attr.

You can use a tower-of-hanoi backup sequence to optimize space and restore
time -- and, of course, optionally compress the files when storing them
into the backup. Run it as a nightly cron job...

Of course you probably aren't wanting this because you already have a daily backup system in place, right? I mean everyone know that comes before considering a mirrored RAID.

:-)
-linda



Hi Linda..
Yes, I do nightly backups of the host system... The reason for
considering the mirror is that it's virtual machines running on VMware
and the host system is using a very high speed SAS array and I simply
would like a hot backup "just in case".

It's really not a big deal since the SAS array is RAID-5 with 2 hot
spare drives, so I'm pretty certain drive failures won't be a problem,
however the risk of disk trashing is always present in case of a
"unclean" shutdown. Then a hot mirror of the VM drives can come in handy, at least for the IMAP and MySQL functions.

I think I'll simply do some experimenting on the matter.. ;-)

Thanks for your feedback!
Anders.


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