SAS5IR performance issue with Dell 860

Espen Tagestad espen at
Sun Nov 25 08:08:10 PST 2007

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 

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?

med vennlig hilsen / with regards,

Espen Tagestad

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