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

[Les Mikesell <lesmikesell@gmail.com>]

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