Extremely slow write speeds to disk : FreeBSD 7.1 and Dell SAS 6/iR Adapter

Tom Judge tom at tomjudge.com
Tue Feb 17 13:43:32 PST 2009

Sebastiaan van Erk wrote:
> Dieter wrote:
>>>> But the issue is that writing to disk is extremely slow...i.e. 14Mb 
>>>> per
>>>> second....
>>>> If I install any other linux distribution, like CentOS, write speek is
>>>> the way it should be..it averages around 190Mb+ per second
>>>> I was hoping if it were at all possible for you to assist me in with a
>>>> later RAID Controller Driver for the SAS 6/iR Adapter
>>> Try:
>>> hw.mpt.enable_sata_wc=1
>>> in /boot/loader.conf and reboot.
>>> Assuming you are using SATA drives, the write cache is disabled by 
>>> default. This reenables it. The mpt manpage holds more information.
>> Just keep in mind that turning the disk's write cache on puts your
>> data at risk.  :-(
>> The correct solution is NCQ.
> Just wondering, if you have a battery on your RAID array, is this a 
> problem? Wouldn't the cache get written anyway in case of a crash?
> Regards,
> Sebastiaan

hw.mpt.enable_sata_wc tunable enables the on disk write cache not the 
controller write cache.


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