We had a pretty similar issue lately with SCSI, and I suspect it's something similar. There are two interrelated issues: - dpkg uses fallocate where it absolutely shouldn't - it creates new files with typically a single write call, so fallocate doesn't help anything, but actively hurts. - For small enough regions ext4 does not create unwritten extents but zeroes data on disk, and whenever zeroing out the data is expensive this really shows up. The SCSI case was a device that has a horrible slow WRITE_SAME implementation, but for nbd we'll just write the zero page repeatedly. Patching out the stupid fallocate in dpkg will speed ext4 up a lot (especially for small files) and will probably speed XFS up a tiny bit as well. But all my mails to the dpkg folks were simply ignored unfortunately. -- 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
