On Mon, Jan 13, 2014 at 02:01:08PM -0700, Andreas Dilger wrote: > Not to be flippant, but is there any reason NOT to just mount the > filesystem with ext4? There are a large number of improvements in > the ext4 code that don't require on-disk format changes (e.g. delayed > allocation, multi-block allocation, etc) if there is a concern about > being able to downgrade to an ext3-type mount in case of problems. I'm leaning towards doing this. The main reason for not doing so was primarily that a few of the tweaks that I had been made to ext3 would have to be ported to ext4. Thankfully, I think we're still in an early enough stage of release that I should be able to do so. The changes are pretty specific, mostly allocator tweaks to improve the on-disk layout for our specific use-case. > There are further improvements in ext4 that can be used on upgraded > ext3 filesystems if the feature bit is enabled (in particular extent > mapped files). However, extent mapped files are not accessible under > ext3, so it makes sense to run with ext4 w/o any new features for a > while until you are sure it is working for you. I had hoped to use ext4, but the recommended fsck after changing the various feature bits is a non-starter during our upgrade process (a 22 minute outage isn't acceptable). > Using delalloc, mballoc, and extents can reduce application visible > read, write, and unlink latency significantly, because the blocks are > being allocated and freed in contiguous chunks after the file is > written from userspace. > > We've been discussing deleting the ext3 code in favour of ext4 for > a while already, and newer Fedora and RHEL kernels are using the > ext4 code to mount ext2- and ext3-formatted filesystems for a while > already. That is reassuring to hear. I'll give it a try and see what happens. -ben > Cheers, Andreas > > > > > -- "Thought is the essence of where you are now." -- 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
