This system is a hardware RAID 6 with I believe 256k strip size set up on it, but a default xfs filesystem on it (mounted with nobarrier, noatime, nodiratime). We do have write-caching enabled on the RAID controller.
> From: [email protected] > Date: Mon, 25 Jul 2011 12:45:02 -0500 > To: [email protected] > Subject: Re: [Samba] Very slow write performance to RAID > > On Mon, Jul 25, 2011 at 12:06 PM, Kevin Taylor > <[email protected]> wrote: > > > > We have a RAID set up as our main fileserver (running samba 3.0.33 on > > linux, CentOS 5). The main disk area is an XFS partition of about 8TB. I'm > > using iostat to monitor disk I/O since we've gotten complaints about speed > > and I'm noticing that when I write something to the samba share, the write > > speed is horrible. For a 15GB file it is reporting to finish in about 20 > > minutes. > > > > With the command: dd if=/dev/zero of=/data/testfile bs=1024k count=10000 > > > > I saw the 10GB write with a speed of 270MB/s, which is decent, so I'm not > > thinking there's anything wrong with the disk or raid controller. > > > > dd isn't really a great test since it's heavily uses caches, and it's > about as sequential as you can get, where samba access is more likely > to be highly random. iometer with dynamo can get you a more "real > workload" type benchmark. > > That said, to me this sounds like a block size and alignment plus > write-back type of issue. Here's some background and examples with > xfs+lvm+mdadm, the base concept apply to hardware raid too > http://www.linux.sgi.com/archives/xfs/2007-06/msg00411.html . Even if > you are getting acceptable perf local, you may be able to get better > if you aren't doing these things, and anything remote will amplify any > latency greatly. > Next toss in windows wanting to flush at 4k or 64k, which should pass > on through to the disk, causing a 128K stripe to flush again with > every 4K, and multiple 128K stripes if things aren't aligned just > right. Then add in the read+modify+write+hash+write operation that > raid5 does and you can start to see where performance can fail. > Hardware raid with battery backed write cache can alleviate this since > it won't wait for the disk spindles. > > Possibly Samba can be tweaked to match your stripe size, I don't know > how off-hand. > -- > To unsubscribe from this list go to the following URL and read the > instructions: https://lists.samba.org/mailman/options/samba -- To unsubscribe from this list go to the following URL and read the instructions: https://lists.samba.org/mailman/options/samba
