Re: [linux-lvm] LVM on SATA/PATA disks

[David Brown <lvm@davidb.org>]

Stuart D. Gathman wrote:

>> How does SATA fit in with all of this?  Is it basically the same
>> limitations on the bus as IDE/PATA, so that you'd really not want to put
>> more than 1 device per bus?
>
> SATA mandates at most 1 disk per channel, making the issue moot.  It is
> still true that there is only one active disk on a bus.  But then there
> is only one disk on a bus.

Newer SATA drives, with proper newer controllers and proper device
driver support will support NCQ (native command queueing), which
allows the drive to re-order requests.  It appears that the Linux ACHI
and Nvidia SATA drivers support this capability in recent kernels.

Of course, any of the re-ordering (SCSI TCQ, or SATA NCQ) requires
filesystem and driver support of write barriers for reliability.
Write barriers are not implement in DM, hence LVM, so there is a
reliability risk in going with this kind of solution.  Depending on
the filesystem this can result in power failures resulting in files
having inconsistent data.

Dave