[CentOS] SATA vs. SAS

[Ross S. W. Walker]

> -----Original Message-----
> From: centos-bounces at centos.org 
> [mailto:centos-bounces at centos.org] On Behalf Of Rajeev R Veedu
> Sent: Wednesday, August 22, 2007 2:52 AM
> To: 'CentOS mailing list'
> Subject: [CentOS] SATA vs. SAS
> 
> I have 8 WD SATA HDD with raid ready (3mbps) hard disks on a 
> 8 port 3ware controller.(on raid 5.) Does anyone have a 
> comparison on SATA raid and SAS raid disk. As you know SAS 
> disk are very expensive and I would like to know from experts 
> in the list who could suggest which of the following would be 
> the best. 

As a lot of people have probably said the answer depends on your
workload.

If the workload is mostly small random io I would go with 15K
SAS configured into a raid10.

If the workload is mostly fairly large sequential reads/writes
(file server) then I would probably go with SATA 7200 RAID5/6
or RAID50/60.

If doing databases set the chunk size to the maximum size of
a data dump i/o (usually 1MB) so each dump i/o hits a separate
spindle, for random it doesn't really matter cause it's random,
you just want the fastest access time money can afford.

For file services you will have to gauge the chunk size by the
type of files, mostly small, small chunks, mostly large, then
larger chunks, 64K is the standard middle-of the road here.

> Option 1) 2 servers each having 2.0TB raid disk with SAS 
> drives, 2GB ram and standard other features. 

If going down this road, why not look into getting one of
those fancy new storage enclosures where the RAID is built
into the enclosure and can allow 2 servers to simultaneously
access the arrays with full battery backed write-back cache?

> Option 2) 4 No servers with 1TB each with 2GB ram and 
> standard other features.

I don't know if I follow you here...

> If Data files (mostly AutoCAD Drawings of size 5MB to 50MB) 
> are distributed as per the above options do you think which 
> could perform better?. As you know the price of SATA disk is 
> much cheaper than the SAS disk and we could nearly by 4 
> servers for that money.

If that's the workload, then save the money and go SATA in a
RAID50 (two RAID5's striped), say a 4-spindle/4-spindle if
you could go to say 10-12 disks then do a 5-spindle/5-spindle
with 1 or 2 hotspares.

> Probability work disturbed by a server crash is low in the 
> second case but I am not sure about the comparison on performance.

Look at a shared storage solution so you can have the storage
fail-over in the even of a server crash rather then replicate
it.

> I would appreciate if you could spread some thought in this 
> regards, and apologize if this is out of topic. 
> 
>  
> 
> Best regards,
> 
>  
> 
> Rajeev
> 
>  
> 
> 

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