SAS Drives

[TRau]

Although I have been using SAS (serial attached SCSI) drives for a few months now, I just recently had a chance to do some side by side comparisons of SAS, SCSI and SATA drives on identical hardware.

The servers were all HP ML350 G4p servers, Xeon 3Ghz processors, 4GB ram, running Server2003 Std. Both the SAS and SATA equipped servers used a HP P600 RAID controller. The SCSI server used a smart array 641. All three were configured with 4 drives in a raid5 configuration with a fifth drive as a hot spare. Both the SCSI and SAS used 72GB drives, the SATA 80GB drives.

As expected the SAS drives out performed both the SCSI and SATA drives. In my simple tests (actually doing baseline performance tests before deployment) the SAS drives were some 40% better than SCSI and over 180% better than SATA.

Have any of you begun using SAS drives? If so what has your experience been? Anybody started using the new 2.5 inch form factor SAS drives?

 

[integrity_host]

SAS datacenter

Do you know any data centers who offer SAS?

 

[TRau]

Do you know any data centers who offer SAS?

No, although I'm sure there must be some that do.
These servers were all business servers for clients that were replacing servers. One of the appealing things about SAS is that SAS raid controllers are backwards compatible with SATA drives. My first use of this technology was for an architectural firm. They wanted a large amount of inexpensive storage (for archived jobs) along with high quality for the main drives. So that server was configured with four SAS drives (raid5 with spare) for the OS and primary storage and two large SATA drives for archived jobs. All on the same backplane using the same controller.
As prices of SAS controllers continue to come down I'm sure more places will begin to offer it. After all, then you can plug in SAS or SATA drives as needed.

 

[spiv]

Very interesting. A few questions --

Are you performance results based on running benchmark programs or actual real-live usage?

For ages I've seen benchmarks that show one technology better than another (e.g. SCSI versus PATA or SATA) but in real-live for "typical" installations where the servers are not pushed to the limit, the actual usage doesn't show much difference a lot of the time.

The mix-and-match of SAS and SATA is intriguing. Am I correct in understanding that this is only possible with a new SAS RAID controller that allows use of SAS or SATA drives wheras an existing SATA-only RAID controller (such as 3Ware) won't work if you try to plug in a newer SAS drive?

Not having seen SAS drives yet, are the physical connectors and cables the same? I.E. will the backplanes and drive cages start to be universal and allow use of SAS or SATA?

 

[TRau]

No, I don't waste time on artifical benchmarks (usually). These tests were all done running real applications and databases to establish baseline performance numbers for the servers (useful for future troubleshooting).

Yes you are correct, only a compatible SAS controller will allow you to add SATA. Keep in mind though that SAS and SATA cannot be mixed on the same array. So you can setup for example a three drive SAS array and a three drive SATA array on the same SAS Raid controller but cant add a SATA drive to the SAS array.

The connectors are the same, on the HP servers I used, the hotswap backplane will accept either a hotswap SAS or SATA drive.