On Wed, 25 Feb 2009, Martin K. Petersen wrote:
"david" == david <david@xxxxxxx> writes:
512-byte logical / 512-byte hardware (current) 512-byte logical /
4096-byte hardware (ATA, doing read-modify-write) 4096-byte logical /
4096-byte hardware (SCSI initially, ATA later)
david> add to this good support for SSDs
david> ?? logical / 128K hardware
david> or similar.
Yep. And that goes for RAID arrays too.
For SCSI there some knobs we can query to get this information and my
alignment changes are using those (and they are in turn what Willy's
stuff hooks into).
I've been lobbying the SSD vendors whose architecture is prone to
misalignment problems to propose a similar set of knobs for ATA. But so
far it's just been a lot of talking.
even if we can't get them to give us any info from the drive directly, we
still want to allow the sysadmin to configure the use of the systems when
they can find the info in other ways.
My topology changes are a bit abstract in the sense that they expose:
- smallest I/O you can submit without incurring a penalty (hw sector,
raid chunk size)
- optimal I/O size for the device in question
- biggest I/O you can submit without incurring a penalty
- alignment
We can use these parameters to lay out partitions and filesystems
optimally. Just like we currently do with XFS but implemented in a more
generic way that all filesystems can use.
if you have the smallest and largest I/O you can submit without a penalty
and the alignment, isn't the optimal I/O size everything between these
two? (or at least everything between these two may be close enough that
defining an 'optimal' size may not be worthwhile)
David Lang
--
To unsubscribe from this list: send the line "unsubscribe linux-ide" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
