Zhihui Zhang wrote:
> My feeling is that if we allocate ALL the data blocks of a big file
> contiguously, this will lead to "too much localization" as described in
> the paper (or the book). However, this may be good for this big file if
> the system buffering capability and hardware allow it (at the cost of
> other files?)
Maybe this is something we could get if XFS is ported: XFS's guaranteed
rate I/O (partly) works by putting guaranteed-rate files on distinct
positions on the disk, or different "subvolumes" in the case of GRIO
on XLV logical volumes. So when preparing a filesystem you could build
a logical volume out of twenty 9 Gbyte disks plus another five 9 Gbyte
disks for guaranteed-rate files.
[ in practice you'd probably be building such a filesystem for a specific
application, though, so you'd probably really use 25 9 Gbyte disks for
GRIO :-) ]
You decide which subvolume a file is allocated to immediately after
file creation: There's an ioctl() which can be used before the first
write to a new file which sets the "please make me fast" flag.
One thing that helps to make this possible is an I/O scheduler which
supports prioritization. Hmm...
- mark
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