Am 23.09.2014 um 15:38 schrieb Austin S Hemmelgarn: > On 2014-09-23 09:06, Stefan G. Weichinger wrote: >> What features for example? > Well, running 'mkfs.btrfs -O list-all' with 3.16 btrfs-progs gives the > following list of features: > mixed-bg - mixed data and metadata block groups > extref - increased hard-link limit per file to 65536 > raid56 - raid56 extended format > skinny-metadata - reduced size metadata extent refs > no-holes - no explicit hole extents for files > > mixed-bg is something that you generally wouldn't want to change after > mkfs. > extref can be enabled online, and the filesystem metadata gets updated > as-needed, and dosen't provide any real performance improvement (but is > needed for some mail servers that have HUGE mail-queues) ok, not needed here > I don't know anything about the raid56 option, but there isn't any way > to change it after mkfs. not needed in my systems. > skinyy-metadata can be changed online, and the format gets updated on > rewrite of each metadata block. This one does provide a performance > improvement (stat() in particular runs noticeably faster). You should > probably enable this if it isn't already enabled, even if you don't > recreate your filesystem. So this is done via btrfstune, right? I will give that a try, for my rootfs it doesn't allow me right now as it is obviously mounted (live-cd, right?). > no-holes cannot currently be changed online, and is a very recent > addition (post v3.14 btrfs-progs I believe) that provides improved > performance for sparse files (which is particularly useful if you are > doing things with fixed size virtual machine disk images). Yes, I have some of those! > AFAIK there isn't really any 'version number' that has any meaning in > the superblock (except for telling the kernel that it uses the stable > disk layout), however, there are flag bits that you can look for > (compat_flags, compat_ro_flags, and incompat_flags). I'm not 100% > certain what each bit means, but on my system with a only 1 month old > BTRFS filesystem, with extref, skinny-metadata, and no-holes turned on, > i have compat_flags: 0x0, compat_ro_flags: 0x0, and incompat_flags: 0x16b. > > The other potentially significant thing is that the default > nodesize/leafsize has changed recently from 4096 to 16384, as that gives > somewhat better performance for most use cases. I have the 16k for both already. Thanks for your explanations, I will dig into it as soon as I find the time. Seems I have to backup/restore quite some stuff ;-) Stefan -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
