On 2010-11-01, at 16:58, Alex Bligh wrote: > --On 1 Nov 2010 15:45:12 Andreas Dilger <adilger.kernel@xxxxxxxxx> wrote: >> What is it you really want to do in the end? Shared concurrent writers >> to the same file? High-bandwidth IO to the underlying disk? > > High bandwidth I/O to the underlying disk is part of it - only one > reader/writer per file. We're really using ext4 just for its extents > capability, i.e. allocating space, plus the convenience of directory > lookup to find the set of extents. > > It's easier to do this than to write this bit from scratch, and the > files are pretty static in size (i.e. they only grow, and grow > infrequently by large amounts). The files on ext4 correspond to large > chunks of disks we are combining together using an device-mapper > type thing (but different), and on top of that lives arbitary real > filing systems. Because our device-mapper type thing already > understands what blocks have been written to, we already have a layer > that prevents the data on the disk before the file's creation being > exposed. That's why I don't need ext4 to zero them out. I suppose > in that sense it is like the swap file case. > > Oh, and because these files are allocated infrequently, I am not > /that/ concerned about performance (famous last words). The performance > critical stuff is done via direct writes to the SAN and don't even > pass through ext4 (or indeed through any single host). Actually, I think Ceph has a network block-device feature (recently submitted/committed to mainline), and Lustre has a prototype block-device feature as well. Cheers, Andreas _______________________________________________ Ext3-users mailing list Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
