Question : Problem: Troubleshooting a performance issue: new SATA drives only getting 7MB/s write

I have an HP ML350 G5 server using an E200i RAID controller w/ 128MB cache and a BBWC.  I have 6 SATA 250GB 7200 RPM drives in a hot-plug drive cage.  This is what I'm getting:

When I set the cache to 0% read / 100% write and perform sequential reads, I get 50MB/s (~400mbps)
When I set the cache to 100% read / 0% write and perform sequential writes, I get 7MB/s (~50mbps)
When I set the cache to 50% read / 50% write, I get good read and write performance

I'm assuming that either:
1) All 6 drives are bad (not very likely)
2) Something's wrong with the integrated E200i controller

I have 3 questions:
1) Are there any other possibilities than above?
2) What is most likely wrong?
3) Would purchasing a P400 RAID controller (411064-B21) probably solve the problem?  If yes, can I hook up the 6-drive hot-plug cage to the controller?

Answer : Problem: Troubleshooting a performance issue: new SATA drives only getting 7MB/s write

As andyalder says, the thing that really, really, really skews benchmark testing is the on-disc cache. Quality RAID controllers turn it off - the reason being that you the OS has no way of knowing if data it has written has actually been physically written to the disc if he on-disc write cache is on. When the on-disc write cache is enabled, the disc firmware returns a "write complete" message to the controller or OS once the write data has been copied into its memory - not onto the disc itself. When the write cache is disabled, the disc firmware has to complete the write to the oxide layer before a "write complete" message can be returned.

>I have tried RAID 1+0 - it performs a little better, but not a whole lot better.  Is this also to your expections?
Maybe. It depends on the number of discs and how clever the RAID controller is. In your case, its probably about right - in terms of the bandwidth available, you only get three discs worth.

>It sounds like an upgrade to a P400 controller would be of little use, with the exception that the bigger cache might be helpful.  Is this correct?
Sorry to say that I don't know the HP product range - but a faster RAID controller with more cache is always good.

>It sounds like the only performance boost I'll get with RAID 5 over JBOD is when multiple processes are maxing out on the volume, in which case the RAID 5's performance will degrade more gracefully, since there are more spindles.  Is this correct?
The big advantage of RAID 5 is redundancy and read performance. Write performance, as you've seen. is limited, especially with personal storage discs. I'd go with RAID 5 for the data integrity and redundancy. If you need better write performance, then perhaps you could consider SCSI or SAS disks - which will give you a major performance boost over the ATA/SATA discs.

One thing you should be aware of, too, is that SATA/IDE disc performance will degrade as you put lots of them next to each other in a cage because they mechanically interact with each other and upset each other's mechanical stability. You don't get this issue with SCSI discs as they're designed to be put into a multiple drive cage. Its one of the many reasons that SCSI discs are more expensive.