SAS5IR performance issue with Dell 860

Tom Judge tom at
Sun Nov 25 08:16:10 PST 2007

Espen Tagestad wrote:
> Tom Judge wrote:
>> Espen Tagestad wrote:
>>> We recently bought 3 new Dell 860 servers with the onboard SAS5/IR 
>>> SATA RAID-controller. They seem to be quite well spec'ed servers with 
>>> management and everything - but I am experiencing av major 
>>> performance issue with the disc i/o. On write I get at max 7-8MB/sec, 
>>> while read gives a bit more (11MB/sec). I tried first with 
>>> 6.2-RELEASE, and then upgraded to 6.3-PRERELEASE without any better 
>>> results.
>> You will also need to set the hw.mpt.enable_sata_wc sysctl in 
>> loader.conf.
> There isn't any hw.mpt.enable_sata_wc sysctl available on my systems. It 
> is 6.3-PRERELEASE, but as I recon there wasn't any *mpt* sysctls on the 
> latest 6.2-RELEASE either. Is it deprecated? Is there any other options? 
> I can see a hw.ata.wc but that one is set to 1 which I presume equals 
> enabled.
> Anyway - the write cache, is that something that is set on the raid 
> controller, or is it a buffer in the FreeBSD kernel that takes care of 
> the caching? As the commit note you sent me said - to ensure absolutely 
> best data integrity the write cache should be left switched off. But 
> write performance of 7-8MB/sec is just too low for that - is the 
> controller /sata drives really that slow?

Please read

You will have to set the sysctl in /boot/loader.conf and reboot the 
system for the changes to take affect.


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