Date: Tue, 10 Aug 2010 12:46:15 +0000 From: "b. f." <bf1783@googlemail.com> To: freebsd-questions@FreeBSD.org Cc: Dick Hoogendijk <dick@nagual.nl> Subject: Re: AHCI driver Message-ID: <AANLkTinsJy4D=PV-rgHw5uumS_cdyFoCYQ5hxtvNHTSC@mail.gmail.com>
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>Is it really better to enable AHCI driver? Almost certainly, yes. If your BIOS and SATA controller use AHCI, and are recognized by the ahci(4), mvs(4), or siis(4) drivers (I think that these drivers are built as kernel modules by default in the recent versions of FreeBSD, and don't require the use of a custom kernel with the non-default ATA_CAM option -- all you have to do is load them at boot time, either manually or via loader.conf(5)), then you will be able to use features like NCQ and better power management with disk drives that support those features. This can give you substantial benefits. If your BIOS and/or SATA controller don't support AHCI, in order to use cam(4) you must build a custom kernel with the ATA_CAM option. In that case you may still see some benefits, but they won't be as dramatic as in the AHCI case. If I recall correctly, the only disadvantage to this option is that it prevents the use of ataraid(4) -- everything else has a (usually slightly better) counterpart with the option, and it is only a matter of configuring your system to use it and learning how to use the new management tools (like camcontrol(8)), rather than the old tools (like atacontrol(8)). And yes, if you use the new drivers or the ATA_CAM option, some of your disks will probably show up as /dev/adaX, rather than the old /dev/adX. So make sure that you adjust fstab(5) and device.hints(5) as necessary before rebooting. b.
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