[CentOS] First Time Setting up RAID

Thu Nov 14 20:52:20 UTC 2013
Mauricio Tavares <raubvogel at gmail.com>

On Thu, Nov 14, 2013 at 1:04 PM, SilverTip257 <silvertip257 at gmail.com> wrote:
> 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?
      Butting in, I know people who would argue for either solution,
and that is not even calling the zfs crowd... ;)

>> >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?
      Servers I have built usually have 2 40GB SSDs in raid1 for the
OS and then SSDs or spinny disks for the data itself in some raid

>> 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.
      I do agree that for the amount of drives he has, raid10 seems to
be the way to go. That said, what about raid6?

>> 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.
      But it would be faster. And disks are cheap.
>> 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
> http://en.wikipedia.org/wiki/Nested_RAID_levels
> I wouldn't suggest nesting software raid if you can avoid it for the
> complexity.
> There are reasons to create a raid array with two hardware arrays, but I'd
> avoid doing so.
>> Comments, suggestions, caveats?
>> Regards,
>> --
>> ***          E-Mail is NOT a SECURE channel          ***
>> James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
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> Mike
> //  SilverTip257  //
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