On 9/23/2011 7:11 PM, Thomas Fjellstrom wrote:
On September 23, 2011, Stan Hoeppner wrote:
On 9/23/2011 11:22 AM, Thomas Fjellstrom wrote:
I'd love to switch, but I didn't really have the money for the card then,
and now I have less money. I suppose if I ebayed this card first, and
then bought a new one that would work out, but yeah, It will have to
wait a bit (things are VERY tight right now).
Which is why you purchased the cheapest SAS card on the market at that
time. :)
So this Intel card, looks like a good option, but how much faster is it?
I get 500MB/s read off this SASLP. Probably a bit more now that there's
7 drives in the array. Off of XFS, it gets at least 200MB/s read (the
discrepancy between raw and over xfs really bugs me, something there
can't be right can it?).
When properly configured XFS will achieve near spindle throughput.
Recent versions of mkfs.xfs read the mdraid configuration and configure
the filesystem automatically for sw, swidth, number of allocation
groups, etc. Thus you should get max performance out of the gate.
What happens when you add a drive and reshape? Is it enough just to tweak the
mount options?
When you change the number of effective spindles with a reshape, and
thus the stripe width and stripe size, you definitely should add the
appropriate XFS mount options and values to reflect this. Performance
will be less than optimal if you don't.
If you use a linear concat under XFS you never have to worry about the
above situation. It has many other advantages over a striped array and
better performance for many workloads, especially multi user general
file serving and maildir storage--workloads with lots of concurrent IO.
If you 'need' maximum single stream performance for large files, a
striped array is obviously better. Most applications however don't need
large single stream performance.
If you really would like to fix this, you'll need to post on the XFS
list. Much more data will be required than simply stating "it's slower
by x than 'raw' read". This will include your mdadm config, testing
methodology, and xfs_info output at minimum. There is no simple "check
this box" mega solution with XFS.
I tweaked a crap load of settings before settling on what I have. Its
reasonable, a balance between raw throughput and directory access/modification
performance. Read performance atm isn't as bad as I remember, about 423MB/s
according to bonnie++. Write performance is 153MB/s which seems a tad low to
me, but still not horrible. Faster than I generally need at any given time.
That low write performance is probably due to barriers to some degree.
Disabling barriers could yield a sizable increase in write performance
for some workloads, especially portions of synthetic benchies. Using an
external log journal device could help as well. Keep in mind we're
talking about numbers generated by synthetic benchmarks. Making such
changes may not help your actual application workload much, if at all.
Given your HBA and the notoriously flaky kernel driver for it, you'd be
asking for severe pain if you disabled barriers. If you had a rock
stable system and a good working UPS you could probably run ok with
barriers disabled, but it's always risky without a BBWC RAID card. If
you want to increase benchy write performance I'd first try an external
log device since SATA disks are cheap. You'll want to mirror two disks
for the log, of course. A couple of 2.5" 160GB 7.2k drives would fit
the bill and will run about $100 USD total.
Thank you for the suggestion though, I will have to book mark that link.
You're welcome.
You can't find a better value for an 8 port SAS or SATA solution that
actually works well with Linux. Not to my knowledge anyway. You could
buy two PCIe x1 4 port Marvell based SATA only cards for $20-30 less
maybe, but would be limited to 500MB/s raw unidirectional PCIe b/w vs
2GB/s with an x4 card, have less features, eat two slots, etc. That
would be more reliable than what you have now though. The Marvell SATA
driver in Linux is much more solid that the SAS driver, from what I've
read anyway. I've never used/owned any Marvell based cards. If I go
cheap I go Silicon Image. It's too bad they don't have a 4 port PCIe
ASIC in their line up. The only 4 port chip they have is PCI based.
Addonics sells a Silicon Image expander, but the total cost for a 2 port
card and two expanders is quite a bit higher than the better Intel
single card solution.
I appreciate the tips. That intel/LSI card seems like the best bet.
It's hard to beat for 8 ports at that price point. And it's an Intel
card with LSI ASIC, not some cheapo Rosewill or Syba card with a
Marvell, SI, JMicron, etc.
--
Stan
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