[CentOS] SATA vs. SAS

[Lamar Owen]

From: Peter Arremann 
>On Wednesday 22 August 2007, Bowie Bailey wrote:
> Peter Arremann wrote:
>> > On the other hand, data reliability is another issue.

>> Why do you say that SATA arrays are less reliable? 

>Not all drive support cache flushes and handle them correctly - even with NCQ. 
>Same for some older controllers also have some issues too. 
>Doesn't show up as a hardware error but as filesystem inconsistency after a 
>crash.  

>As I wrote, we haven't had issues yet either. But sun, sgi, ibm and others are 
>fairly conservative  - sun says they still only ships 500GB disks in their 
>x4500 for that reason. 

EMC and IBM are shipping Seagate Barracuda ES 750GB drives now.  Just bought and installed two CLARiiON CX3-10c's with two DAE3's each, full of 750GB SATA II drives (the interesting thing is that the DAE is still 4Gb/s FC; the SATA carriers have an emulex bridge board translating the FC-AL to SATA II on the carrier; the DAE's are FC all the way).  The IBM DS4200 is available with SATA II.  I chose EMC due to software features and VMware support 'stuff' even though it was quite a bit more $$ per TB.  We have two 20TB systems at this point.

Performance is excellent, at least according to bonnie++.  I expected random access to suffer due to the 7200 RPM drives (versus what 15K drives would have been), and it did.  Block writes from a CentOS 4 VM  through ESX's multipathing through two Qlogic 4Gb/s PCIe 4x FC controllers was 125MB/s or so, RAID5 5 drive RAID groups and 1.95TB LUNs.

EMC and IBM both made it clear that they consider SATA second tier well below FC; but FC is, of course, much more expensive.
--
Lamar Owen
Chief Information Officer
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772
828-862-5554
www.pari.edu