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Re: RAID setups, usage, Q's' effect of spindle groups...etc...blah blahb

To: Linda Walsh <xfs@xxxxxxxxx>
Subject: Re: RAID setups, usage, Q's' effect of spindle groups...etc...blah blahblah...
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Mon, 21 Jan 2013 21:02:58 -0600
Cc: xfs-oss <xfs@xxxxxxxxxxx>
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On 1/21/2013 11:12 AM, Linda Walsh wrote:
> 
>> If nothing else I hopefully got the point across as to how destructive
>> parity RAID read-modify-write operations are to performance.  It's
>> simply impossible to get good mixed IO performance from parity RAID
>> unless one's workloads always fit in controller write cache, or if one
>> has SSD storage.
>>
> 
> ----
> Will have to reread it a few times to digest everything (but it is
> sufficiently
> depressing...)...

Depressing?  If someone explained to me how I could get a 2x-50x
increase in performance just by rearranging what I already had, I'd say
that's exciting, not depressing.  If 24TB net isn't sufficient for a 1
person home office/media setup then you must be doing something unique.

> Especially the costs on the enclosures...I am pretty sure I paid under
> 1k for
> each of them....*ouch*...

Keep in mind that big Norco is 24 bays for ~$1400.  So it's still
considerably less per bay than the two 630Js you bought, not even taking
the devalued dollar into account.  Note the small cost difference
between the 12 and 24 bay Norcos is due to the SAS expander module being
~$700 of the unit price.  The 24 has a little more sheet metal, 3 more
backplane PCBs, 12 carriers, and a slightly larger PSU-- all low cost
items, $230 retail cost.

Maybe worth pondering:  for ~$3900 one can acquire that Norco chassis
filled with 24x 1TB SATA 7.2K UltraStars.  Performance would be the same
as I described for your current 24 drives in RAID10.  You'd have 12TB
net.  Simply jack it into the spare port on your 9280 or daisy chain it
off a 630J.  You'd then use it for everything but say your media files.
 For those you'd reconfigure your current 24x 2TB drives into a concat
of two 12 drive RAID6 arrays.  This would yield 40TB net for media, and
since it's a primarily single streaming workload 10 effective RAID6
spindles would yield great performance, maximum space, with dual parity
reliability.

$3900 is a decent chunk to part with in one shot.  But with the
resulting high performance 12TB space for work and 40TB for play, I'd
think you'd thrive for many, many years without needing to worry about
storage performance or space.

A trap many/most home users fall into is buying such a chassis and 4
drives in RAID5, then adding sets of 4 drives in RAID5 as "budget
permits", and ending up with 6 separate arrays thus 6 different data
silos each of low performance.  This may be better/easier on the wallet
for those who can't/don't plan and save, but in the end they end up with
1/6th of their spindle performance for any given workload, and a
difficult migration path to get the actual performance the drives are
capable of.  Which is obviously why I recommend acquiring the end game
solution in one shot and configuring for maximum performance from day one.

-- 
Stan

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