On Sun, Aug 17, 2014 at 10:29:21PM -0500, Stan Hoeppner wrote: > Say I have a single 4TB disk in an md linear device. The md device has a > filesystem on it formatted with defaults. It has 4 AGs, 0-3. I have > created 4 directories. Each should reside in a different AG, the first in > AG0. Now I expand the linear device with an identical 4TB disk and execute > xfs_growfs. I now have 4 more AGs, 4-7. I create 4 more directories. > > Will these 4 new dirs be created sequentially in AGs 4-7, or in the first > 4 AGs? Is this deterministic, or is there any chance involved? On the Deterministic, assuming single threaded *file-system-wide* directory creation. Completely unpredictable under concurrent directory creations. See xfs_ialloc_ag_select/xfs_ialloc_next_ag. Note that the rotor used to select the next AG is set to zero at mount. i.e. single threaded behaviour at agcount = 4: dir number rotor value destination AG 1 0 0 2 1 1 3 2 2 4 3 3 5 0 0 6 1 1 .... So, if you do what you suggest, and grow *after* the first 4 dirs are created, the above is what you'll get because the rotor goes back to zero on the fourth directory create. Now, with changing from 4 to 8 AGs after the first 4: dir number rotor value new inode location (AG) 1 0 0 2 1 1 3 2 2 4 3 3 <grow to 8 AGs> 5 0 0 6 1 1 7 2 2 8 3 3 9 4 4 10 5 5 11 6 6 13 7 7 14 0 0 > real system these 4TB drives are actually 48TB LUNs. I'm after > deterministic parallel bandwidth to subsequently added RAIDs after each > grow operation by simply writing to the proper directory. Just create new directories and use the inode number to determine their location. If the directory is not in the correct AG, remove it and create a new one, until you have directories located in the AGs you want. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
