Smart Array P400 Drive Failure

Question

I have a HP Proliant server with a Smart Array P400 RAID controller with 2 146 gb 10k SAS hard drives configured in a mirrored RAID configuration. Where could I find information regarding how a drive failure would affect this configuration? I am looking to see how this RAID configuration and hardware would react to a drive failure.

Answer 1

I'd start here: HP Smart Array P400 controller - Questions & Answers

Honestly though almost every decent RAID controller acts the same in the case of a single drive failure in a two disk RAID 1 array. Since the Smart Array is a true hardware RAID controller either drive can fail and the OS will still work just about as fast as it did with two drives. If you had a software based RAID controller (Some of the cheaper Promise models for instance) then you sometimes need a boot diskette to force booting off the second drive.

The HP Smart Array's are very good RAID controllers, they are decently fast, very reliable and dead simple to use. They are definitely my favorite embedded RAID controller. One great feature they have is being able to pull a set of drives from one system and stick it into another for recovery etc. purposes. Lot's of other RAID controller get very confused when you present them an array pulled from a different controller, not so the Smart Array. They just work!

Answer 2

Couple of statements grabbed from the HP Smart Array Controller technology technology brief has a few insights:

RAID 1 load balancing

In general, RAID 0, RAID 5, and RAID 6 with ADG logical drives have the same read performance given the same stripe size and array size. RAID 1 logical drives contain two copies of the data. During reads to RAID 1 logical drives, the Smart Array controller issues read requests to either drive in the mirrored set. During a heavy read load, the Smart Array controller balances the number of requests between the two hard drives to achieve higher read bandwidth. This technique is called RAID 1 load balancing.

Automatic data recovery with rapid rebuild technology ... Generally, a rebuild operation requires approximately 15 to 30 seconds per gigabyte for RAID 5 or RAID 6 with ADG logical drives (where gigabytes are the measured capacity of the replacement disk drive). However, actual rebuild time depends on several factors, including the amount of I/O activity occurring during the rebuild operation, the number of disk drives in the logical drive, the rebuild priority setting, and the disk drive performance.

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So, while it's rebuilding, it'll try and do it in-between regular disk IO, but it will have some impact on performance.

Answer 3

Typically you may see some degraded read performance should a drive failure, but there will be no loss of service. Additional degradation may be seen when you replace the faulty drive and the array rebuilds.

Were you after some more specific information? :)

Answer 4

I fully agree with what Ausmith1 wrote. Both HP and IBM use the P400. That should tell you a lot about the quality and reliability.

The only thing I would suggest changing is the addition of a hot spare. Then, if a drive goes bad the controller will simply swap in the spare and, assuming you have things configured appropriately, you will get some alerts telling you what's happening. The users should never even be aware a drive has failed. If the users do notice a degradation while the array is rebuilt you may be running too close to the edge and should perhaps look at something like RAID 5.