On Mon, Jan 13, 2014 at 04:16:10PM -0500, Benjamin LaHaise wrote: > > 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. We have been thinking about making some changes to the block allocator, so I'd be interested in hearing what tweaks you made and a bit more about your use case that drove the need for these allocator tweaks. > 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). You can move to ext4 without necessarily using those features which require an fsck after the upgrade process. That's hwo we handled the upgrade to ext4 at Google. New disks were formatted using ext4, but for legacy file systems, we enabled extents feature (maybe one or two other ones, but that was the main one) and then remounted those file systems using ext4. We called file systems which were upgraded in this way "ext2-as-ext4", and our benchmarking indicated that for our workload, that "ext2-as-ext4" got roughly half the performance gained when comparing file systems still using ext2 with newly formated file systems using ext4. Given that file systems on a server got reformatted when it needs some kind of hardware repairs, betewen hardware refresh and disks getting reformatted as part of the refresh, the percentage of file systems running in "ext2-as-ext4" dropped fairly quickly. Mike Rubin gave a presentation about this two years ago at the LF Collab Summit that went into a lot more detail about how ext4 was adopted by Google. That presentation is available here: http://www.youtube.com/watch?v=Wp5Ehw7ByuU Cheers, - Ted -- 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
