[TriLUG] Re: New system configuration thoughts

[Kevin Jones]

That's interesting. I wonder what other user's experiences have been with this? The two drives I lost in the RAID 5 array were actually both U160 SCSI drives made by HP...go figure. The only problems I've ever had with SATA drives were from the desktop-grade (non-RAID) drives I had unwittingly put in an array. It was a RAID 6 array, however, so it didn't pose any real issue. 

I was put in charge of acquiring an enterprise-grade array at my last job (approx. 2 years ago) and at that time, no one had anything good to say about SATA except in highly redundant systems that could withstand multiple failures. In fact, the prices seemed to reflect the same 3:1 ratio across the board suggesting the SCSI folks knew that they could charge 3 times the cost of a SATA drive and get away with it. Perhaps that has changed now. 

Kevin

----- Original Message ----
From: Lance A. Brown <lance at bearcircle.net>
To: Triangle Linux Users Group discussion list <trilug at trilug.org>
Sent: Thursday, May 3, 2007 12:28:21 PM
Subject: [TriLUG] Re: New system configuration thoughts


RATS.  Forgot the footnote.

Kevin Jones wrote:
> To get RAID 6, you need to have a RAID 6 capable Host Bus Adapter 
> (HBA). I have set them up on HP DL3xx servers that come with a 
> built-in HBA and also on Adaptec SATA HBA's. Most newer RAID cards 
> have RAID 6 capability. SCSI drives are definitely the way to go for 
> enterprise-class storage (particularly with high I/O activity such as
>  databases) as the MTBF (mean time between failure) rate is MUCH 
> better with SCSI than (S)ATA drives (approx. 3 years for SCSI vs. 1 
> year for SATA on average I think.) In other words, plan on buying 
> three SATA drives for every one U320 SCSI drive. Also, be very 
> careful about the SATA drives you purchase if putting them in a RAID 
> array as there is a very big difference between desktop-grade and 
> enterprise (RAID-level)-grade SATA drives. Unfortunately, the vendors
>  probably don't know and manufacturers don't make this point clear, 
> but SATA is reasonably new to the enterprise and you can get stuck 
> with really crappy drives if you buy the wrong kind.

The distinction between SCSI and SATA drives may not be as strong as you
state it.  The "Best Paper" award recipient from the 5th USENIX
Conference on File and Storage Technologies is entitled 'Disk Failures
in the Real World: What Does an MTTF of 1,000,000 Hours Mean to You?'[1]
and contains the following:

   It is interesting to observe that for these data sets there is no
   significant discrepancy between replacement rates for SCSI and FC
   drives, commonly represented as the most reliable types of disk
   drives, and SATA drives, frequently described as lower quality. For
   example, the ARRs of drives in the HPC4 data set, which are
   exclusively SATA drives, are among the lowest of all data sets.

The accepted wisdom about the difference between SCSI and SATA drives
may not be accurate.

--[Lance]

[1]
http://www.usenix.org/events/fast07/tech/schroeder/schroeder_html/index.html


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