Choosing the right RAID was Re: [ILUG] Wee nas box

[David Guerin]

> Message: 9
> Date: Fri, 20 Nov 2009 11:18:47 +0000
> From: Gavin McCullagh <gmccullagh at gmail.com>
> Subject: Choosing the right RAID was Re: [ILUG] Wee nas box
> To: ilug at linux.ie
> Message-ID: <20091120111847.GF19029 at gmail.com>
> Content-Type: text/plain; charset=iso-8859-1
> 
> Hi,
> 
> On Fri, 20 Nov 2009, Pádraig Brady wrote:
> 
>> Hardware RAID is worse than software RAID right?
>> See the last paragraph here:
>> http://www.pixelbeat.org/docs/hard_disk_reliability/#RAID
> 
> This is a question I come to regularly.  Opinion seems very divided and I'm
> not sure a general answer to the question exists.
> 
> I would side with good software raid (such as linux md) over cheap hardware
> RAID.  However battery-backed hardware RAID seems valuable and I've yet to
> see a solution to that with software RAID -- apart from a UPS perhaps.
> I've also repeatedly heard the performance benefits of hardware RAID are
> considerable (I'm not sure I've ever seen data to back this up though).
> 
> There are those who are critical of md too:
> 
> 	http://www.ashtech.net/~syntax/blog/archives/53-Data-Scrub-with-Linux-RAID-or-Die.html
> 	http://www.nber.org/sys-admin/linux-nas-raid.html
> 
> The other question I have is whether to trust RAID5.  There appear to be
> some people who really think not and:
> 
> 	http://www.miracleas.com/BAARF/RAID5_versus_RAID10.txt
> 	http://www.baarf.com/
> 
> the former article is even distributed as part of the Debian mdadm package.
> 
> I recently asked this question of a techie/sales guy who looked at me as
> though I had 5 heads (he was pushing a 3-drive RAID5 unit).  As far as he
> was concerned, RAID5 is _the_ industry standard and he had never seen a
> problem (beyond the usual single drive failure) in the countless installs
> he had been involved in.
> 
> Is this a real concern?  In terms of a budget, in some instances you could
> probably use SCSI drives in RAID5 to achieve the same capacity as SATA
> drives in RAID1.
> 
> I'm just dying for someone to tell me the "real truth".
> 

Well for the most part I would agree with Hardware RAID. If you get a "good" RAID Controller that is pretty versatile in its configuration (I tend to go for a mid ranged Adaptec, around €350 for 8 Sata/SAS ports), it think that can be the best option, because it abstracts away the messy RAID configuration that can be required if you go with md on linux, (especially if a disk fails and you have to rebuild the raid to the new disk). There are other nice features like RAID5EE for automatically rebuilding the raid should a disk ever go pop.

Though recently I tried a Software RAID 1 on this Quad Core Zeon Box with two 750 Gig SATA disks. And I was absolutely astonished how much data I was getting through to the disks per second when I compared it to the RAID5 I have with a Hardware RAID, en fact it was almost double what the Hardware RAID was doing across a Gigabyte LAN. (I know its not the best comparison since different RAIDs but the speed of reading and writing to the Software RAID was enough for me to consider it in future, where as I would not have bothered before).

Regards
Dave