HP Smart Array p400i with Intel X25-M 160 SSD

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I have a pair of x25-M 160 Intel SSD's in an HP DL360 G5 with a p400i Smart Array running 512 BBWC. The disk performance I am getting on this box and another identical one does not come close to matching the same two drives running through a cheap 3ware RAID card. Any idea?

I have played with the cache settings, but nothing allows me to get the same results. It seems like the Smart Array controller is the bottleneck.

Best Answer

You may want to consider using another disk measurement tool. Have The p400 controller and HP SAS disks are very common setups, and if you were only receiving 5MB/s random reads/writes, there may be a larger problem. Can you run your analysis using another disk performance analysis program like Iometer?

For the SSD drives, I'd expect a better random read/write, but it helps to understand exactly what you're testing.

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A few thoughts;

SSDs have 'overcommit' memory. This is the memory used in place of cells 'damaged' by writing. Low end SSDs may only have 7% of overcommit space; mid-range around 28%; and enterprise disks as much as 400%. Consider this factor.
How much will you be writing to them per day? Even middle-of-the-range SSDs such as those based on Sandforce's 1200 chips rarely appreciate more than around 35GB of writes per day before seriously cutting into the overcommitted memory.
Usually, day 1 of a new SSD is full of writing, whether that's OS or data. If you have significantly more than >35GB of writes on day one, consider copying it across in batches to give the SSD some 'tidy up time' between batches.
Without TRIM support, random write performance can drop by up to 75% within weeks if there's a lot of writing during that period - if you can, use an OS that supports TRIM
The internal garbage collection processes that modern SSDs perform is very specifically done during quiet periods, and it stops on activity. This isn't a problem for a desktop PC where the disk could be quiet for 60% of its usual 8 hour duty cycle, but you run a 24hr service... when will this process get a chance to run?
It's usually buried deep in specs but like cheapo 'regular' disks, inexpensive SSDs are also only expected to have a duty cycle of around 30%. You'll be using them for almost 100% of the time - this will affect your MTBF rate.
While SSDs don't suffer the same mechanical problems regular disks do, they do have single and multiple-bit errors - so strongly consider RAIDing them even though the instinct is not to. Obviously it'll impact on all that lovely random write speed you just bought but consider it anyway.
It's still SATA not SAS, so your queue management won't be as good in a server environment, but then again the extra performance boost will be quite dramatic.

Good luck - just don't 'fry' them with writes :)

Slow DL360 Smart Array P400i RAID

This is several questions in one, so I'll try to address a few of them.

I typically set Smart Array controllers to leverage a higher write cache ratio. I prefer to have 75% write cache because the OS (using the XFS filesystem) caches aggressively. XFS will make a difference, but what are you tuning for? Are you tuning to simply achieve specific numbers, or is there an application requirement driving this?

ext3 isn't the fastest filesystem out there. But you have some mount options (e.g. noatime) and journal settings you could tweak.
I don't use LVM, especially with HP controllers that can provide many of the same benefits.
You have I/O scheduler and elevator settings (e.g. noop or deadline, in this case) that can be tuned, but that's a function of your application's actual needs.

If you do go with XFS, try a basic config then try some advanced configuration settings. Over time, I've ended up with mount parameters very similar to the one in the original link.

I just ran the following iozone command line on an XFS partition contained within a DL380 G5 with P400i, 12GB RAM and 8 x 146GB 10k drives. The elevator is set to deadline:

Command line used: iozone -t1 -i0 -i1 -i2 -r1m -s24g

initial writers  =  348957.75 KB/sec
rewriters        =  335130.03 KB/sec
readers          =  132851.70 KB/sec
re-readers       =  137116.27 KB/sec
random readers   =   35774.41 KB/sec
random writers   =  250618.38 KB/sec

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