Software RAID 5 or something else?

[Dave Stevens]

On Friday 23 January 2009 09:39:44 am aragonx at dcsnow.com wrote:
> Hello all,
>
> I had a drive failure a few months back so I decided it was time to rework
> my home server's storage.
>
> Now I have 5 750GB SATA dives and now I need some advice on how to set
> things up.
>
> My original idea was to put them in a RAID 5 configuration.  This sounded
> good until I started researching RAID controller cards.  It looks like it
> will cost me $520 to get a good PCI-E card (3Ware 8 port).  I don't think
> I want to spend that much if I don't have to.
>
> My goals are two fold.
>
> 1) I want to get some redundancy in case of a drive failure.
>
> 2) I want to increase my performance.  I have benchmarked my read and
> write performance to and from this server.  Using Samba, I seem to be able
> to get about 50Mb/sec reads and 40Mb/sec writes.  I am on a gig network
> and would like to be able to max out the cards (90Mb/sec is what I get at
> work).
>
> So, the question is, what should I do?
>
> 1)  Bite the bullet and get the hardware RAID controller.  Will this give
> me the performance I want?
>
> 2)  Go with a software RAID 5.  Will I lose performance with this
> configuration?  If I use this but only get modest performance gains, that
> would be acceptable.
>
> 3)  Go with some other software RAID level.
>
> Any help would be appreciated.
>
> ---
> Will Y.

I think you want software raid. The little processor on a hardware raid card 
is unlikely to be better that what you already have for a cpu. If the hw raid 
card breaks for any reason you may be faced with trying to find just the same 
card and revision number to regain access to your data, a distressing 
experience no matter what. SW raid can confidently be expected to be stable 
over time. 

On point 1 I think you can look for blogs like the storage report and have a 
look at anandtech.com for reviews of raid including performance figures. On 
point 2 I think you will gain performance. The stipulated gain from 50 to 90 
MB/sec seems quite achievable. On point 3 I think you need to look at testing 
others have performed to see what is the best (to you) combination of raid 
level, safety and speed.

I might add that I have a currently working F7 implementation on a single 
Seagate 320 SATA drive and hdparm -tT shows 78 MB/sec reads  while on another 
new drive, a Seagate 640 SATA I get 110 MB/sec. No raid at all and the only 
drive in the system. It might be worthwhile to examine your current setup 
further for bottlenecks before spending that kinda coin.

Dave

>
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