twa driver and 3ware 9690SA issues
andrew at modulus.org
Mon Mar 2 14:51:04 PST 2009
Josh Paetzel wrote:
> Which wasn't that much of an issue, as SATA drives aren't capable of
> sustained sequential 100 MB/sec transfers anyways
As Scott said, this number is not reflective of actual negotiated rate,
and is nothing to worry about.
> u0 RAID-10 OK - - 64K 596.025 ON OFF
> 838860800 bytes transferred in 6.923690 secs (121158052 bytes/sec)
> Kind of what I expect, and faster than 100 Megs/sec
Well, that's a RAID10 and capable of doing much faster than 120MB/s.
Sorry, but you cannot expect anywhere near close to the theoretical
unformatted maximum media transfer rate of the disks you're testing,
especially under FreeBSD and UFS.
Testing the raw disks doesn't necessarily help either because then
there's no operating system read-ahead or write-caching, which is
necessary to lower the latency between access requests.
I don't believe you're getting any SCSI or 3ware problems - just FreeBSD
kernel and filesystem issues.
UFS is performance is a bit bizarre: for example I see faster sequential
write speeds than read speeds! ZFS improves the situation alot and I get
much closer to the theoritical max with my drives.
To give you an idea of how much more efficient ZFS is: I had a 16 disk
3ware SATA RAID6, with UFS, and battery-backed cache. I converted to a
14 disk ZFS software RAIDZ2 with a smaller 3ware mirrored boot disk.
Quick benchmarked using dd as follows:
Creating a 6GB file: UFS+3ware=308mb/s ZFS=357mb/s
Reading a 6GB file: UFS+3ware=113mb/s ZFS=424mb/s
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