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

Sebastiaan van Erk sebster at sebster.com
Fri Feb 13 23:58:14 PST 2009

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?

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