[CentOS] First Time Setting up RAID

Thu Nov 14 18:04:28 UTC 2013
SilverTip257 <silvertip257 at gmail.com>

On Thu, Nov 14, 2013 at 12:23 PM, James B. Byrne <byrnejb at harte-lyne.ca>wrote:

> Arch = x86_64
> CentOS-6.4
> We have a cold server with 32Gb RAM and 8 x 3TB SATA drives mounted in
> hotswap
> cells.  The intended purpose of this system is as an ERP application and
> host.  The ERP application will likely eventually have web access but at
> the
> moment only dedicated client applications can connect to it.
> I am researching how to best set this system up for use as a production
> host
> employing RAID.  I have read the (minimal) documentation respecting RAID on
> the RedHat site and have found and read a few online guides.  Naturally,
> in my
> ignorance I have a bunch of questions to ask and I probably have a bunch
> more
> that I should but do not know enough yet to ask.

Are you going to use hardware or software raid?

> >From what I have read it appears that the system disk must use RAID 1 if
> it
> uses RAID at all.  Is this the case?  If so, is there any benefit to be
> had by
> taking two of the 8 drives (6Tb) solely to hold the OS and boot partition?
> Should these two drives be pulled and replaced with two smaller ones or
> should
> we bother with RAID for the boot disk at all?
> Given that one or two drive bays will be given over to the OS what should
> be
> the configuration of the remaining six?  It appears from what I have read
> that
> RAID 5 is the only viable option.  It also appears that the amount of
> storage

What about RAID10?

I've read that running a database server on raid5 isn't recommended, but
raid1 or raid10 is recommended.

> available on a RAID5 array with N members is N-1/N. I also read that as the
> number of members increase both latency and the risk of data loss
> increases.
> As the amount of disk space we have in this unit (24Tb) is greater than the
> total storage of all our existing hosts it appears that a RAID5 array of 5
> units would leave at least one hot spare in the chassis and two if the OS
> is
> put on one disk.

Space efficiency is less than that of raid5.
Rather than 1-1/n with raid5 you have 2/n with raid10.

> Alternatively, the thought comes to mind that we could do a RAID1 with two
> RAID5 arrays each of which have 3 drives.  Whether one would actually want
> to
> do that seems to me a bit questionable but it seems to be at least
> possible.

You're suggesting a raid5+1 or raid51

I wouldn't suggest nesting software raid if you can avoid it for the
There are reasons to create a raid array with two hardware arrays, but I'd
avoid doing so.

> Comments, suggestions, caveats?
> Regards,
> --
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> James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
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//  SilverTip257  //