On 7/31/13 12:28 PM, Bill McGonigle wrote: > >> Adding a mount option, "-o journal_path=/dev/$DEVICE" would help, >> since then we can do i.e. >> >> # mount -o journal_path=/dev/disk/by-label/$JOURNAL_LABEL /mnt > > I came here with a related problem, and I wonder if it would be a > more general solution to this one too. > > I've got a machine with root on ext4 on LUKS on md, and while I was > first planning to use flashcache or dm-cache underneath it (for SSD > acceleration) I saw benchmarks that convinced me that an external > journal on ext4 was the better option. > > It's getting it mounted at boot time that's the trick. > > I saw that tune2fs supports '-J device=UUID=foo-bar-baz', so I setup > a LUKS volume on the SSD, formatted it, passed it in, and it sets up > the journal fine when I'm booted from external media, but when I > reboot under the OS (3.10 in Fedora 19 in this case) it fails to > mount because the device number has changed. > > I see the proper UUID listed in 'tune2fs -l' - the "Journal UUID" is > right, but "Journal device" is no longer correct, so boot fails until > I remove the journal again. Neat eh? ;) > I think with LUKS, I'm never guaranteed > to get a consistent device ID between boots, so the kernel command > line options don't help either. > > So, I was thinking, that if the ext code did: 1) try stored journal > device ID 2) on fail, look up the UUID via libblkid 3) perhaps update > the stored device ID well, kernelspace can't use libblkid. > it would solve my problem. I wonder if it would be a more robust > solution to the problem posed here as well (having the filesystem > contain its own references is better IMHO). My one handy system that > has an ext3 volume (still on Fedora 16, e2fsprogs-1.41) does not show > a Journal UUID flag via 'tune2fs -l', but I'm unaware of whether the > flag is unavailable/missing/unsupported there or if it could be > added. I think my patch will solve your problems as it is, just add the new mount option to fstab, remake your init$WHATEVER, and off you'll go. I'll send the ext4 version in a minute if you want to try it. -Eric > -Bill > -- 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
