Peter Arremann wrote:
On the other hand, data reliability is another issue. We have tons of sata based disk arrays and have had no issues yet (because our systems are all on UPS and multiple circuits) but if you don't have infrastructure like that, you are more likely to lose data on a sata based system...
Why do you say that SATA arrays are less reliable? I have used both SATA and SCSI raid and have had drive failures on both. Recovery from the failures seems to be more a matter of the raid implementation than the interface type.
On Wednesday 22 August 2007, Bowie Bailey wrote:
Peter Arremann wrote:
On the other hand, data reliability is another issue. We have tons of sata based disk arrays and have had no issues yet (because our systems are all on UPS and multiple circuits) but if you don't have infrastructure like that, you are more likely to lose data on a sata based system...
Why do you say that SATA arrays are less reliable? I have used both SATA and SCSI raid and have had drive failures on both. Recovery from the failures seems to be more a matter of the raid implementation than the interface type.
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.
Peter.
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
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Bowie Bailey -
Lamar Owen -
Peter Arremann -
Ray Leventhal