io - Acceptable I/O speeds for 6 x 250GB SSDs in RAID 10

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I'm running CentOS 7 (XFS filesystem)
on a dell server with a PERC H700 raid controller. Inside this server I have 6 x Samsung
850 Evo 250GB SSDs (yes they are consumer drives however, this is a home server. In any
case, I performed a DD test and am getting speeds of around 550MB/s which would be the
approximate write speed of a single SSD yet these drives are in RAID 10.... where one
would expect more.

Output of a
write
test:

[root@localhost]
            sync; dd if=/dev/zero of=tempfile bs=1M count=1024; sync
1024+0 records
            in
1024+0 records out

1073741824 bytes (1.1 GB) copied,
            1.95942 s, 548
            MB/s

Output
of a read
test:

[root@localhost]#
            dd if=tempfile of=/dev/null bs=1M count=1024
1024+0 records
            in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 0.171463 s,
            6.3
            GB/s

Would
anyone be able to shed some light on this situation as to whether this is an acceptable
write speed? I'm rather puzzled as to what to do here.
Appreciate your help
:)

Answer

href="https://serverfault.com/a/431456/13325">I could close this as a
duplicate because there are a lot of factors that impact storage performance
in Linux.

I think people have the wrong idea
when they attempt to benchmark SSD performance. You should use SSDs for better random
I/O performance. You're testing big-block sequential performance, which doesn't match
any sort of use case except for, um, copying large
files.

• Throughput:
  Maximum bandwidth (likely sequential) of the
  array.



• IOPS: How
  many I/O operations per second the array is capable
  of.


• Latency: How quickly the
  storage subsystem can service your I/O
  requests.

The last two
are what matter in most cases. Add to this the fact that you're using a RAID controller,
there is an element of caching at play. Also, XFS and Linux cache I/O, so you need to
know what you're testing.

I'd suggest using a
purpose-built tool like fio, iozone or
even bonnie++ to run a proper set of
benchmarks.

Also see: href="https://serverfault.com/questions/431437/hp-p410-raid-samsung-830-ssds-debian-6-0-what-performance-to-expect/431456#431456">HP
P410 RAID + Samsung 830 SSDs + Debian 6.0 - What performance to
expect?