twa driver and 3ware 9690SA issues

Andrew Snow andrew at
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

- Andrew

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