Well, I tried to convert my non-/home space to XFS with an external journal,
but Linux consistently choked on it. I passed "rootfstype=xfs root=/dev/sdb5
rootflags=logdev=/dev/sda2" on the kernel command line (via GRUB) but it
panicked every time.
Here is a transcript of the boot panic from an unmodified kernel:
md: Autodetecting RAID arrays.
md: Scanned 0 and added 0 devices.
md: autorun ...
md: ... autorun DONE.
XFS: Invalid device [/dev/sda2], error=-2
VFS: Cannot open root device "sdb5" or unknown-block(8,21)
Please append a correct "root=" boot option; here are the available partitions:
0800 390711384 sda driver: sd
0801 1005448 sda1
0802 3008880 sda2
0803 30005640 sda3
0804 1 sda4
0805 356688328 sda5
0b00 1048575 sr0 driver: sr
0810 488386584 sdb driver: sd
0811 146488671 sdb1
0812 4008217 sdb2
0813 3004155 sdb3
0814 1 sdb4
0815 334882926 sdb5
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,21)
Judging from the output, it seems not to be able to open the log device
/dev/sda2. I slipped in a couple statements in xfs_vfsops.c to watch for
function entries and successful exits. I saw where xfs_blkdev_get() was called
twice, the first time successfully (probably corresponding to /dev/sdb5), the
second time unsuccessfully (/dev/sda2). Yet, the partition list at the end of
the panic shows /dev/sda2 as recognized and available.
Is this a known issue?
As an acceptable substitute, I moved /usr to XFS with an external journal.
Staying with the deadline scheduler, it's a noticeable difference. OOo launches
in about 4 seconds.
"What better place to find oneself than
on the streets of one's home village?"
--Capt. Jean-Luc Picard, "Family"