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Wed, 20 Aug 2008
To SSD or not to SSD? High-end SSD vs. SAS disks benchmark.
There is a lot of hype around SSD these days... People frequently belive that it is a panacea for
hard drive problems related to random disk access. Let's see, how high-end SSDs behave comapred
to SAS disks.
I got access to IOzone benchmark performed by Vladislav Seliverstov
from Yandex team.
Tested disks: SSD MTRON MSP-SATA7035 (7000?), maximum read speed: 120 MB/s, write speed: 90 MB/s, access latency: 0.1 ms.
Rotating disk was Fujitsu SAS MBA3147RC.
Tests were performed on ext3 filesystem woth the following options (stride option differs accordingly in RAID tests):
# mke2fs -b 4096 -R stride=16 -j -J size=384 -m 0 -O dir_index /dev/md0Mount options:
/dev/md0 /mnt/raid ext3 noatime,reservation,data=writeback,commit=300 0
dirty_writeback_centisecs VM sysctl was set to 3000.First, single disk performance: SAS vs SSD.
Sequential access speed (both reading and writing) is almost 20% higher for SAS disk than that of SSD. But let's look at random access speed.
SSD reading jumps to the maximum theoretical 100-120 MB/s plato very quickly (impressive peaks at 64 and 128 KBs, which can tell us a bit of the firmware structure of the data blocks), SAS disk is definitely a looser here, since it reaches its maximum performance numbers only at 8-16 MB records.
But SSD random writing is more than two times slower than that of SAS until the latter reaches its maximum performance.
Also very intersting to note, that sequential access is actually noticebly slower than the maximum random access speed for SSD.
Now let's check two-SSD-disk SW RAID-0 array performance with different stripe size.
Random read peaks move around depending on stripe size.
So clearly if your workload depends on random writing, SSD may not be an appropriate solution, and it is definitely the winner in random reading workload. Please also note, that it was high-end SSD with 0.1 ms seek latency, and dight now most of the popular SSDs do not have that shiny numbers.
Great thanks to Vladislav Seliverstov for his data and analysis.
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