Hi Dave,
On 01/11/2018 10:14 AM, Dave Chinner wrote:
Are you telling me that xfs is aware of the internal structure of an
md-raid array?
It's aware of the /alignment/ characteristics of block devices, and
these alignment characteristics are exported by MD. e.g. These are
exported in /sys/block/<dev>/queue in
minimum_io_size
- typically the stripe chunk size
optimal_io_size
- typically the stripe width
We get this stuff from DM and MD devices, hardware raid (via scsi
code pages), thinp devices (i.e. to tell us the allocation
granularity so we can align/size IO to match it) and any other block
device that wants to tell us about optimal IO geometry. libblkid
provides us with this information, and it's not just mkfs.xfs that
uses it. e.g. mkfs.ext4 also uses it for the exact same purpose as
XFS....
I see xfs can detect the geometry with "sunit" and "swidth", ext4 and gfs2
can do similar things as well.
I have one question about xfs on top of raid5. Is it possible that multiple
write operations happen in the same stripe at the same time? Or with the
existence of those parameters, xfs would aggregate them, then it ensures
no conflict happens to the parity of the stripe. Thanks in advance!
Regards,
Guoqing
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