Mailinglist Archive: opensuse (2324 mails)

[Anders Norrbring <lists@xxxxxxxxxxxx>]

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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