P2000 G3 SAS - disk reporting wrong transfer rate.

[Whitestar261]

Good afternoon, we have had a P2000 SAS device for some time now, with dual controllers and are very pleased with it (in general) However, we've recently put 6x 300Gb 15krpm 6Gb SAS disks into a new RAID5 vDisk, and one of the disks is only
reporting a Transfer Rate of 3Gb. All the others report as 6Gb. The disks are all recent purchases, and individually the disk reports as a 6Gb - just adding it to the array seems to drop its rate down.

This vDisk is not in use at the moment so i can rebuild it if needs be. Do I need to try to report this as a faulty disk?

Any advice would be appreciated.

Regards

Derrick

[Johan Guldmyr · Accepted solution]

Hello,

if the disk is exactly the same as the other disks (same spare part, model number, firmware, etc, just to be sure you didn't get a slightly different one when you bought it) and if it's speed is also turned down to 3g in another disk bay it sounds like it could be the disk that's the problem.

[Whitestar261]

Johan,

many thanks for your response (and your understanding - it isn't an easy thing to explain) I will try the disk in another bay later today.

The disk does show as a 6Gb disk when it is in stand-alone or spare mode - as soon as it joins an array, the transfer rate drops.

Will post my feedback as soon as possible.

With kind regards

Derrick

[Whitestar261]

Johan,

thanks for your patience. I have now swapped the disks over, and all looks fine (as it did before) UNTIL I configured a RAID-5 Array including ports 19-24 (remember the 3Gb transfer rate was showing up on port 23?)
Each of the disks is exactly the same, and some even have (almost) sequential serial numbers. Firmware versions, Hardware versions identical.

With ports 19-23 in a Raid 5 array, all the ports appeared as 6Gb transfer rates. Port 24 was not added at this time (and indeed was holding the disk previously in port 23)

I added the disk from Port 24 into the array, and surprisingly Port 23 again showed as only running at 3Gb. Maybe it is the enclosure that is at fault?

I worked around this by having a 4 disk RAID5 array of 300Gb disks, and a smaller RAID1 mirror of 2x 300Gb disks. Storage space has been reduced, but  Transfer rates are all showing as 6Gb, and the two smaller disks work just as well for our requirements.

Thanks for your pointers, Johan. Helped me isolate the issue, even if it didn't resolve anything. And it taught me more about my MSA as well.. Consider this answered.

Thanks

Derrick

[Johan Guldmyr]

Whitestar261, I'm glad to help out :)

Really odd that by adding one disk to the array, another disk in a specific/next bay is down-throttled.

Could be something in the enclosure, but there's quite a few things in there: backplane/midplane/controller and more.

Is performance so much lower with "only" 3Gb transfer rate for one disk that it's worth creating this raid1?

These ports, do they correspond so that port 24 is bay 24 (the last down right)?

[Sebastian.Koehler]

Don't rely on the speed reporting in MSA2000/P2000 since this is not a reliable indicator all the time. Replacements are usually not required. From the P2000 CLI reference guide.

show disks

Rate*(Gb/s)
Data transfer rate in Gbit/second. A footnote indicates that it is normal behavior for the rate to vary. Some 6-Gbps disks might not consistently support a 6-Gbps transfer rate. If this happens, the P2000 controller automatically adjusts transfers to those disks to 3 Gbps, increasing reliability and reducing error messages with little impact on system performance. This rate adjustment persists until the controller is restarted or power-cycled.

http://bizsupport2.austin.hp.com/bc/docs/support/SupportManual/c02520779/c02520779.pdf

Regards,
Sebastian