While attempting to recover an unjournalled filesystem last week, it
occurred to me that it should be possible to store the XFS log on a
simple solid-state device. A USB keychain or thumb drive immediately
suggested itself, and a quick check of the XFS manual pages indicated
this is a distinct possibility.
A little talk on a local LUG list pointed out that these things often
have a limited number of write cycles, typically in the millions. One
poster suggested that write levelling could reduce the impact of this
limitation, by increasing the amount of data which can be written to
the device before it starts to fail.
If I can find a system to sacrifice I may be tempted to give this a
try---small drives are fairly cheap and have write cycles large enough
to make a test worthwhile. My XFS-related questions are:
0) Will this really be useful? My hope is that storing the log on a
device which doesn't use the IDE bus will save the log from
becoming corrupted when the IDE disks start to fail. (The restore
I alluded to above would probably have been recoverable if the
disk's superblock and bad block list had remained intact.)
1) How much space will I need, relative to the space required for the
filesystem itself? My home system has an XFS filesystem on /home
which is 1.7GB, and the internal log is about 5MB. Can I expect
this to scale? On a similar note, will acting as an XFS journal
simply exhaust the drive in a matter of months, instead of having a
lifetime comparable to the drives themselves?
2) What sort of performance penalty can I expect to contend with? I
would probably use a USB2.0 drive---fortunately the small ones are
still remarkably inexpensive.
3) Is there some other technology suitable for the small office
situation which might fill this need?
--
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http://www.panix.com/~jasonp
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