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



David Brown wrote:
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.

Are you saying that LVM on SCSI is not safe in this scenario?

--
  Les Mikesell
   lesmikesell gmail com


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