Jerry,
If you wish to avoid the recovery method, you can still use an external log
with your RAID. If you're using hardware RAID, where the array spans the
entire drive, create two partitions on the array (sda1 and sda2, where sda2
is used for the log and is less than 256MB). If you're using software raid,
then it's just as easy. Just create a couple of partitions on each drive in
the array. You'll then create an md1 stripe across one set of partitions
for data and another stripe (md2) on another set of partitions for metadata.
You can then use the following: mkfs.xfs -l logdev=/dev/sda2,size=32000b
/dev/sda1. You can substitute md1 and md2 accordingly.
It won't matter that you're creating a metadata device and a data device on
the same physical set of drives. You're still creating a new page buffer
for the new logical device and this is where you'll speed up performance.
The performance hit of physical disk seeks should be negligible. I've
actually benchmarked the difference between putting the journal on other
RAID stripes, other raids, fast disks, NVRAM, etc. You really shouldn't
notice much difference. Plus, placing the log on another stripe is pretty
cheap to do.