Rich Freeman <ri...@gentoo.org> writes: > On Fri, Jan 9, 2015 at 4:02 PM, lee <l...@yagibdah.de> wrote: >> Rich Freeman <ri...@gentoo.org> writes: >> >>> On Mon, Dec 29, 2014 at 8:55 AM, lee <l...@yagibdah.de> wrote: >>>> >>>> Just why can't you? ZFS apparently can do such things --- yet what's >>>> the difference in performance of ZFS compared to hardware raid? >>>> Software raid with MD makes for quite a slowdown. >>>> >>> >>> Well, there is certainly no reason that you couldn't serialize a >>> logical volume as far as design goes. It just isn't implemented (as >>> far as I'm aware), though you certainly can just dd the contents of a >>> logical volume. >> >> You can use dd to make a copy. Then what do you do with this copy? I >> suppose you can't just use dd to write the copy into another volume >> group and have it show up as desired. You might destroy the volume >> group instead ... > > You can dd from a logical volume into a file, and from a file into a > logical volume. You won't destroy the volume group unless you do > something dumb like trying to copy it directly onto a physical volume. > Logical volumes are just block devices as far as the kernel is > concerned.
You mean I need to create a LV (of the same size) and then use dd to write the backup into it? That doesn't seem like a safe method. >> How about ZFS as root file system? I'd rather create a pool over all >> the disks and create file systems within the pool than use something >> like ext4 to get the system to boot. > > I doubt zfs is supported by grub and such, so you'd have to do the > usual in-betweens as you're eluding to. However, I suspect it would > generally work. I haven't really used zfs personally other than > tinkering around a bit in a VM. That would be a very big disadvantage. When you use zfs, it doesn't really make sense to have extra partitions or drives; you just want to create a pool from all drives and use that. Even if you accept a boot partition, that partition must be on a raid volume, so you either have to dedicate at least two disks to it, or you're employing software raid for a very small partition and cannot use the whole device for ZFS as recommended. That just sucks. >> And how do I convert a system installed on an ext4 FS (on a hardware >> raid-1) to ZFS? I can plug in another two disks, create a ZFS pool from >> them, make file systems (like for /tmp, /var, /usr ...) and copy >> everything over. But how do I make it bootable? >> > > I'm pretty sure you'd need an initramfs and a boot partition that is > readable by the bootloader. You can skip that with btrfs, but not > with zfs. GRUB is FSF so I doubt they'll be doing anything about zfs > anytime soon. Otherwise, you'll have to copy everything over - btrfs > can do in-place ext4 conversion, but not zfs. Well, I don't want to use btrfs (yet). The raid capabilities of brtfs are probably one of its most unstable features. They are derived from mdraid: Can they compete with ZFS both in performance and, more important, reliability? With ZFS at hand, btrfs seems pretty obsolete. -- Again we must be afraid of speaking of daemons for fear that daemons might swallow us. Finally, this fear has become reasonable.
