HP P420i SSD RAID Configuration

Question

I've been testing a HP DL380p with 16x SSDs in a RAID5 on the P420i controller with 2GB FBWC that is integrated on the board. Quite good performance, but not good enough. When I simulate the IO footprint I expect on ESXi, the Average Device Latency goes through the roof - 150 ms. What could cause this?

1. Could the RAID controller be limiting the performance? If so, should I buy a second one?
2. Would it be a good idea to swap to RAID 10 instead? For lower write penalty.

Solution 1

16 disks (especially SSDs) in RAID5 is a bad idea... The HP P420i Smart Array controller would have warned you about this when you created the Logical Drive.

There's some finesse needed to tuning the server you're describing. Can you provide specifics on the SSDs you're using, the current controller settings, the host's firmware levels and your testing methodology?

Also, what type of performance are you expecting versus what you're experiencing?

Solution 2

16 disks in a RAID5 is really bad. And you surely got a warning that you were above 14 disks when you created it? You are using SSDs to get speed, why nullify this in some way by using a RAID5? You need space, buy bigger disks? Too expansive, maybe it is time to review your needs and solution. Use RAID10 (8 pairs of RAID1 SSDs) to stay safe and be the fastest you could possible be with 16 SDDs.

Why is it bad to go over 14 disk in a RAID5 is because when one disk will fail (eventually), the rebuilding that will occur will be terrible. On regular HDDs, you are almost certain to fail another disk while the rebuild occurs and thus losing the entire array. With SSD, you're 'aging' faster and getting them nearer to their UBER (Unrecoverable Bit Error Read) and your array will simply crash there too.

Comments

[AndersN]

Yes, it did, in fact - telling me that best practice for RAID5 includes a maximum of 14 disks, I think. But that's more an issue of safety, I suppose? I use Samsung EVO 500 GB for the drives. This has worked great for me in the past with fewer disks, though. P420i firmware version 5.42. No specific settings other then defaults. I would like to mention that SSD SmartPath is enabled.

[ewwhite]

@AndersN You haven't stated or helped quantify your problem. What is the actual issue?