[TriLUG] Re: New system configuration thoughts

[Jason Tower]

yes, all raid 5.  one of the 15 disk arrays has had a failed disk replaced 
w/ no downtime, the other has had no failed disks at all.

i *think* raid 6 is supported on the newer cards, but haven't really 
checked.  i know you can assign a failover drive, which yields similar 
results as long as you don't lose the second disk before the failover is 
added to the array.

jason

Kevin Jones wrote:
> Is that RAID 5? 
> 
> 
> ----- Original Message ----
> From: Jason Tower <jtower at cerient.net>
> To: Triangle Linux Users Group discussion list <trilug at trilug.org>
> Sent: Thursday, May 3, 2007 3:40:22 PM
> Subject: Re: [TriLUG] Re: New system configuration thoughts
> 
> 
> with a good 3ware controller, sata raid rocks.  i have at least four systems 
> that have been flawless, including two 4TB arrays consisting of 15 disks 
> each.  my primary xen server (currently running ten domUs) also runs 
> beautifully on top of a 3ware controller.
> 
> jason
> 
> Kevin Jones wrote:
>> 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
>>
>>