On 16 May 2010 02:02, Tomasz Torcz <tomek@xxxxxxxxxxxxxx> wrote: > On Sat, May 15, 2010 at 06:47:22PM +0200, Sebastian 'gonX' Jensen wrote: >> >> Would it be possible and feasible to support mounting btrfs >> >> raid/multi-device filesystems without having to run 'btrfsctl -a'? >> >> >> >> Currently, as you may know, if a one wants to attach a btrfs raid >> >> filesystem to a system (usb, hotswap, reboot, etc), the user or program >> >> has to run: >> >> >> >> btrfsctl -a (or similar) >> >> mount /dev/sdb1 /mount/point >> >> >> >> While this works, it will require patching of various subsystems >> >> involved with managing disks, such as udev, mkinitrd, dracut, hal, and >> >> others. Each one will have to know to scan, then mount. >> > >> > In a my previous post ([RFC] btrfs, udev and btrfs - 16/April 2010), I >> > suggested a solution for this kind of problem. I a Debian/Ubuntu system it is >> > not necessary to patch anything, it is only required to put some files in the >> > initramfs-tool configure directories. >> > >> > IIRC, also the md (RAID) subsystem require a scan from the user space to find >> > and activate the volumes. I think also dm (LVM) subsystem requires the same. >> > >> >> md does not require a scan from userspace with at least both RAID-0 >> and RAID-1. There's a setting in the kernel config you can set, which >> will automatically detect all RAID drives with the FD partition flag >> set. DM may however be true. > > > MD will only detect RAID on MS-DOS partitions (seldom used when RAIDing > whole devices, not possible to use with devices >2 TiB) and metadata > 0.90, which is not default. Userspace probing is general way kernel > subsystem are going, it is more flexible. > And dracut already has btrfs module. > You're right, only metadata 0.9 is supported with autodetection kernel-side. I had forgotten about that. On a more related note, I agree that userspace probing is a lot more flexible, but for mounting root partitions it is also extremely inconvenient. I don't know if I mentioned it before, but my system spends at least 6 seconds in the initramfs before passing control over to my distributions initscripts. Part of it is obviously because of btrfs having to spend approximately 3 seconds probing for devices (I have a decent amount of devices). However, btrfs does not have that many functions yet. Would it be possible to at least have partial functionality kernel side, so that an initramfs is not required for mounting RAID devices? > -- > Tomasz Torcz ,,If you try to upissue this patchset I shall be seeking > xmpp: zdzichubg@xxxxxxxxx an IP-routable hand grenade.'' -- Andrew Morton (LKML) > > -- > 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 > -- 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
