On Friday March 29, dean-list-linux-kernel@arctic.org wrote: > 2.4.19-pre3-ac1 > > /dev/md1 is a raid5 of 4 disks > > i was trying out examples from the LVM HOWTO using /dev/md1. in > particular while i was growing a volume/filesystem, i was also creating > a snapshot of the same volume. i.e. > > e2fsadm -L+1G /dev/arctic/home > > and > > lvcreate -L1G -s -n snap.home /dev/arctic/home > mount /dev/arctic/snap.home /mnt/snap.home > > were running at the same time. > > this resulted in lots of log spam of the form: > > Mar 29 10:47:45 debian kernel: raid5: switching cache buffer size, 0 --> 512 > Mar 29 10:47:45 debian kernel: raid5: switching cache buffer size, 0 --> 4096 > Mar 29 10:47:45 debian kernel: raid5: switching cache buffer size, 4096 --> 512 The current raid5 requires all requests that is recieves to be the same size. If it gets requests of different sizes, it does cope but it needs to flush its stripe cache and start again. This effectively serialises all requests around a request-size change. So it is probably fair to say that what you are trying to do is currently not a supported option. It may be in 2.6 if we ever get raid5 working again in 2.5 :-) You could simply remove the printk and recompile and it might go a bit faster, but you would still be loosing lots of performance due to lost opportunities for concurrency. NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
