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From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To: Dieter BSD <dieterbsd@gmail.com>
Subject: Re: IBM blade server abysmal disk write performances
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>
> That is incorrect.  A UPS reduces the risk, but does not eliminate it.

nothing eliminate all risks.

> But for most applications, you must have the write cache off,
> and you need queuing (e.g. TCQ or NCQ) for performance.  If
> you have queuing, there is no need to turn the write cache
> on.
did you tested the above claim? i have SATA drives everywhere, all in ahci 
mode, all with NCQ active.




> It is inexcusable that FreeBSD defaults to leaving the write cache on
> for SATA & PATA drives.  At least the admin can easily fix this by
> adding hw.ata.wc=0 to /boot/loader.conf.  The bigger problem is that
> FreeBSD does not support queuing on all controllers that support it.
i must be happy as i never had a case of not seeing
adaX: Command Queueing enabled
on my machines.