Apologies for my prematurely sent email (if it gets through), this one
is complete...
Hi all,
I've spent a number of years trying to build up a nice RAID array for my
SAN, but I seem to be slowly solving one bottle neck only to find
another one. Right now, I've identified the underlying SSD's as being a
major factor in that performance issue.
I started with 5 x 480GB Intel 520s SSD's in a RAID5 array, and this
performed really well.
I added 1 x 480GB 530s SSD
I added 2 x 480GB 530s SSD
I now found out that performance of a 520s SSD is around 180 times
faster than a 530s SSD. I had to run many tests, but eventually I found
the right things to test for (which matched my real life results), and
the numbers were nothing short of crazy.
Running each test 5 times and average the results...
520s: 70MB/s
530s: 0.4MB/s
OK, so before I could remove and test the 520s, I removed/tested one of
the 530s and saw the horrible performance, so I bought and tested a 540s
and found:
540s: 6.7MB/s
So, around 20 times better than the 530, so I replaced all the drives
with the 540, but I still have worse performance than the original 5 x
520s array.
Working with Intel, they swapped a 530s drive for a DC3510, and I then
found the DC3510 was awesome:
DC3510: 99MB/s
Except, a few weeks back when I placed the order, I was told there is no
longer any stock of this drive, (I wanted 16 x 800GB model), and that
the replacement model is the DC3520. So I figure I won't just blindly
buy the DC3520 assuming it's performance will be similar to the previous
model, so I buy 4 x 480GB DC3520 and start testing.
DC3520: 37MB/s
So, 1/3rd of a DC3510, but still better than the current live 540s
drives, but also still half the original 520s drives.
Summary:
520s: 70217kB/s
530s: 391kB/s
540s: 6712kB/s
330s: 24kB/s
DC3510: 99313kB/s
DC3520: 37051kB/s
WD2TBCB: 475kB/s
* For comparison, I had a older Western Digital Black 2TB spare, and ran
the same test on it. Got a better result than some of the SSD's which
was really surprising, but it's certainly not an option.
FYI, the test I'm running is this:
fio --filename=/dev/sdb --direct=1 --sync=1 --rw=write --bs=4k
--iodepth=1 --runtime=60 --time_based --group_reporting
--name=IntelDC3510_4kj1 --numjobs=1
All drives were tested on the same machine/SATA3 port (basic intel
desktop motherboard), with nothing on the drive (no fs, no partition,
nothing trying to access it, etc..).
In reality, I tested iodepth from 1..10, but in my use case, the
iodepth=1 matches is the relevant number. At higher iodepth, we see
performance on all the drives improve, if interested, I can provide a
full set of my results/analysis.
So, my actual question... Can you suggest or have you tested any Intel
(or other brand) SSD which has good performance (similar to the DC3510
or the 520s)? (I can't buy and test every single variant out there, my
budget doesn't go anywhere close to that).
It needs to be SATA, since I don't have enough PCIe slots to get the
needed capacity (nor enough budget). I need around 8 x drives with
around 6TB capacity in RAID5.
FYI, my storage stack is like this:
8 x SSD's
mdadm - RAID5
LVM
DRBD
iSCSI
From my understanding, it is DRBD that makes everything a iodepth=1
issue. It is possible to reach iodepth=2 if I have 2 x VM's both doing a
lot of IO at the same time, but it usually a single VM performance that
is too limited.
Regards,
Adam
--
Adam Goryachev Website Managers www.websitemanagers.com.au
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