The "xFS Project Architecture" design document has the following to say
about the requirements made on disk driver by XFS:
Disk drivers are the same as in traditional and current IRIX systems,
except for ordering constraints needed by the log and volume managers
and rate guarantees. In particular, it must be possible for the volume
manager to be certain that a write request has actually been completed,
not merely cached for later writing. It should also be possible for the
volume manager to specify that a given write not be reordered - that all
blocks passed to the driver before this block will be written before
this block is written, and all blocks passed to the driver after this
block will be written after this block. (If non-ordered writes are not
available on a particular driver, the volume manager can synthesize
this behavior by waiting for completion, but this is much less efficient.)
I assume the following still holds true. To my knowledge only IBM's IDE
drives support those semantics. Does this mean that all log-writes on
non-IBM IDE drives are synchronous? How does the volume manager know
whether or not the disk driver supports this behaviour?
Thanks.
-Kip
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Kip Macy kmacy@xxxxxxxxxxxxxxx
University of California, Berkeley
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