[CentOS] SDA and HDA

Robert Heller heller at deepsoft.com
Thu Aug 19 18:14:02 UTC 2010

At Thu, 19 Aug 2010 09:54:32 -0500 CentOS mailing list <centos at centos.org> wrote:

> > With the default settings in my Supermicro motherboard CentOS calls my
> > SATA drive /dev/hda.  If in bios setup I change 'Native Mode
> > Operation' from auto to 'Serial ATA' it boots up calling the drive
> > /dev/sda.  I keep thinking its likely better under /dev/sda not?  Any
> > problem switching it to that after install?
> So I guess another question here.  Is it better to my SATA interface
> in Serial ATA mode or AUTO in BIOS?  The motherboard calls it sda when
> in serial ata mode but hda when in auto mode.  Will there be a
> performance difference?

Yes. SATA is going to be faster. Note: your 'motherboard' is not
calling it sda or hda.  What your motherboard is doing is either
*native* Serial ATA mode or *emulated* Parallel ATA (aka IDE) mode
(also known as 'legacy' mode).  The linux *kernel* then either sees IDE
disk(s) (*emulated* Parallel ATA mode) or native Serial ATA disks, and
loads a Serial ATA driver, which uses the SCSI disk abstraction layer
(sd). The *native* Serial ATA mode is faster and more feature-rich,
such as including things like hot-swapping, should you install a SATA
hot-swap bay. This is not possible with IDE disks and the IDE disk
driver does not really support it. Also, motherboards with more than 4
SATA ports will only make 4 available when in 'IDE' mode.  If there are
more than 4 SATA ports on your motherboard, you need to be in native
SATA mode to use all of them.  This includes any E-SATA ports as well.

The only problems with switching after install is:

1) you need to be sure the initrd has the (proper) SATA kernel module(s)
in it.  If necessary, you'll have to use mkinitrd to re-create the
initrd file to include the proper driver modules.

2) /etc/fstab needs to be fixed, either to use LABEL= (rather than
/dev/hdaN) and your file systems (including swap) need to have file
sytem labels.  (LVM volumes won't be a problem.)

> Matt
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Robert Heller             -- 978-544-6933
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