Messages in this thread | | | Date | Fri, 19 Apr 2002 09:08:14 +0100 | Subject | Re: Bio pool & scsi scatter gather pool usage | From | Joe Thornber <> |
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On Fri, Apr 19, 2002 at 02:29:25AM -0500, Stephen Lord wrote: > But this gets you lowest common denominator sizes for the whole > volume, which is basically the buffer head approach, chop all I/O up > into a chunk size we know will always work. Any sort of nasty boundary > condition at one spot in a volume means the whole thing is crippled > down to that level. It then becomes a black magic art to configure a > volume which is not restricted to a small request size.
This is exactly the problem; I don't think it's going to be unusual to see volumes that have a variety of mappings. For example the 'journal' area of the lv with a single fast pv, 'small file' area with a linear mapping across normal pv's, and finally a 'large file' area that has a few slower disks striped together.
The last thing I want in this situation is to split up all the io into the lowest common chunk size, in this case the striped area which will typically be < 64k.
LVM and EVMS need to do the splitting and resubmitting of bios themselves.
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