Date: Fri, 18 Jan 2013 21:39:24 +0100 (CET) From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl> To: Dieter BSD <dieterbsd@gmail.com> Cc: freebsd-hackers@freebsd.org, gibbs@freebsd.org, scottl@freebsd.org, mjacob@freebsd.org Subject: Re: IBM blade server abysmal disk write performances Message-ID: <alpine.BSF.2.00.1301182137070.13253@wojtek.tensor.gdynia.pl> In-Reply-To: <CAA3ZYrBV9f%2BcHx4jvS0UKTr%2Bp7eNUBA0S2%2Bv9oZAHqwm9VBOWw@mail.gmail.com> References: <CAA3ZYrBV9f%2BcHx4jvS0UKTr%2Bp7eNUBA0S2%2Bv9oZAHqwm9VBOWw@mail.gmail.com>
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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.
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