> > A reshape is a fundamentally slow operation. Each block needs to > be read and then written somewhere else so there is little opportunity > for streaming. > An in-place reshape (i.e the array doesn't get bigger or smaller) is > even slower as we have to take a backup copy of each range of blocks > before writing them back out. This limits streaming even more. > > It is possible to get it fast than it is by increasing the > array's stripe_cache_size and also increasing the 'backup' size > that mdadm uses. mdadm-3.1.1 will try to do better in this respect. > However it will still be significantly slower than e.g. a resync. > > So reshape will always be slow. It is a completely different issue > to filesystem activity on a RAID array being slow. Recent reports of > slowness are, I think, not directly related to md/raid. It is either > the filesystem or the VM or a combination of the two that causes > these slowdowns. > > > NeilBrown > stripe_cache_active = default 0? stripe_cache_size = default 256? (1mb per disk) cat /sys/block/md52/md/stripe_cache_* 0 8192 I bumped it up, but I haven't seen a real increase in the speed yet. Do I need to mdadm -S /dev/md52 and then re-assemble it to have this take effect, or is it the fact that the stripe cache active seems to be 'deactivated'? Can I safely set this to 1 mid-reshape? -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
