On Jun 29, 2007 18:26 -0400, Mike Waychison wrote: > Andreas Dilger wrote: > >I don't think ext2 is safe for > 8TB filesystems anyways, so this > >isn't a huge loss. > > This is reference to the idea of overloading the high-bit and not > related to the >PAGE_SIZE blocks correct? Correct - just that the high-bit use wouldn't unduely impact the already-existing 8TB limit of ext2. The other thing to note is that Val Henson already ported the ext3 reservation code to ext2, so this is a pretty straight forward option for you and also doesn't affect the on-disk format. > >The other possibility is, assuming Google likes ext2 because they > >don't care about e2fsck, is to patch ext4 to not use any > >journaling (i.e. make all of the ext4_journal*() wrappers be > >no-ops). That way they would get extents, mballoc and other speedups. > > We do care about the e2fsck problem, though the cost/benefit of e2fsck > times/memory problems vs the overhead of journalling doesn't weigh in > journalling's favour for a lot of our per-spindle-latency bound > applications. These apps manage to get pretty good disk locality > guarantees and the journal overheads can induce undesired head movement. You could push the journal to a separate spindle, but that may not be practical. > ext4 does look very promising, though I'm not certain it's ready for our > consumption. FYI, the extents code (the most complex part of ext4) has been running for a couple of years on many PB of storage at CFS, so it is by no means new and untried code. There are definitely less-well tested changes in ext4 but they are mostly straight forward. I'm not saying you should jump right into ext4, but it isn't as far away as you might think. > What are people's thoughts on providing ext3 non-journal mode? We could > benefit from several of the additions to ext3 that aren't available in > ext2 and disabling journalling there sounds much more feasible for us > instead of trying to backport each ext3 component to ext2. This is something we've talked about for a long time, and I'd be happy to have this possibility. This would also allow you to take similar advantage of extents, the improved allocator and other features. Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc. - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
