Very poor performance from Dell/LSI Logic SAS 3000 series SATA/SAS RAID controller FreeBSD 6.3

[Chris Dillon]

Quoting Scott Long <scottl at samsco.org>:

> For data reliability, you really don't want it enabled by default.  The
> problem is that SATA/ATA performs so poorly without it that everyone
> turns it on and lives with the consequences.  The tweak that I
> recommended puts it in line with what the FreeBSD ATA driver has been
> doing for years.

Doesn't SATA NCQ solve this particular performance vs. reliability  
problem since it safely allows multiple outstanding write requests?   
Of course that means the SATA RAID controller would have to use NCQ on  
the drives and would probably also need its own non-volatile cache.   
I've always assumed this is how SCSI/SAS drives (with TCQ) perform as  
well as they do without sacrificing data integrity.

We recently bought a new HP DL380G5 server with a P800 SAS RAID  
controller, MSA60 external drive shelf with 12 750GB SATA drives,  
11-drive RAID5 array w/ hot-spare (a few too many drives in a single  
RAID5 array, I know, but I'm experimenting).  The system is running  
Windows Server 2K3 R2.  Without telling the P800 to enable the SATA WC  
(it has an option to do so, off by default), when doing a drag and  
drop file copy of several very large files from the internal SAS array  
to the external SATA array it writes 300MB/sec.  I briefly enabled the  
"Physical Drive Write Cache" on the controller just a few minutes ago  
and ran another test and didn't notice any difference in write speed.   
I can only assume from this that the P800 is using NCQ on the SATA  
drives.

-- 

Chris Dillon - NetEng/SysAdm
Reeds Spring R-IV School District
Technology Department
175 Elementary Rd.
Reeds Spring, MO  65737
Voice: 417-272-8266   Fax: 417-272-0015