I'm working with a Supermicro SMC2208 raid controller.
To increase the capacity of a large RAID array, I decided to add two additional disks using storcli. storcli /c0/v0 start migrate type=raid6 option=add drives=2:12,2:14
The problem is, I did not expect that this would disable the "read ahead" read policy, the write-back cache and the pdcache, which all together slow down the system considerably.
So the first question is already: Is this cache turnoff expected after the above command? I never saw this mentioned.
Is there a way to stop the migration/expansion process, to delay it, pause it or anything? It would take very long to complete and with the read ahead cache off, it becomes too slow. At least it would be good to pause it during some hours. I'm aware of the migraterate
parameter, but even when that is set to 1, the performance is slow.
I tried removing these disks again by storcli /c0/v0 start migrate type=raid6 option=remove drives=2:12,2:14
but it won't stop the current migration:
-------------------------------------------------------------------------
VD Operation Status ErrCd ErrMsg
-------------------------------------------------------------------------
0 MIGRATE Failed 50 device state doesn't support requested command
-------------------------------------------------------------------------
Pausing also doesn't seem to be an option storcli /c0/v0 pause migrate
-----------------------------------------------------
VD Operation Status ErrCd ErrMsg
-----------------------------------------------------
0 Migrate Failed 255 Pause Migrate not possible
-----------------------------------------------------
And during the migration/reconstruction it seems impossible to use the read ahead cache policy: storcli /c0/v0 set rdcache=ra
----------------------------------------------------------
VD Property Value Status ErrMsg ErrCd
----------------------------------------------------------
0 rdCache RA Failed reconstruction in progress 29
----------------------------------------------------------
Unfortunately the full rebuild would take 12 days according to the controller's estimate and it would be very annoying to keep the server this slow for that long.