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[dm-devel] IO errors when tuning max_sectors_kb value of a dm device



 Hi all,

If dm-devel is the good list to ask questions, could anyone have a look at my problem ?

I observe some IO errors on a multipath device for which the max_sectors_kb parameter has been tunned. Value is increased from the default (1024) to the value of the hw max sectors (32768).

The following error appears in the system log:
1301326968 2011 Mar 28 17:42:48 berlin4 kern err kernel blk_rq_check_limits: over max size limit.
Followed by several I/O errors
1301326968 2011 Mar 28 17:42:48 berlin4 kern err kernel end_request: I/O error, dev dm-10, sector 26624 1301326968 2011 Mar 28 17:42:48 berlin4 kern err kernel end_request: I/O error, dev dm-10, sector 24576 1301326968 2011 Mar 28 17:42:48 berlin4 kern err kernel end_request: I/O error, dev dm-10, sector 22528
    ...

I have seen in the device-mapper source code that when a multipath device is configured, its limits are computed from a combination of all the slave devices it uses (dm_calculate_queue_limits()).

Does it mean that tuning the dm device is forbidden ?
Is there way to re-validate the queue limits after the tuning ?

Do you think it would be safe if I additionally tune the max_sectors_kb parameter of the slave devices ?

Thanks in advance,
Gregoire.





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