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I'm considering a new install/upgrade, and I thought I'd like to try JFS as my file system this time. From what I've read, an external journal gives better performance, but I have a few questions.
First, can different partitions share an external journal, or does each partition require its journal to be in a separate partition?
Scenario A (shared journal) would be: / on /dev/sda1 with journal on /dev/sdb1, /usr on /dev/sda2 with journal on /dev/sdb1, and /home on /dev/sda3 with journal on /dev/sdb1.
Scenario B (individual journals) would be: / on /dev/sda1 with journal on /dev/sdb1, /usr on /dev/sda2 with journal on /dev/sdb2, and /home on /dev/sda3 with journal on /dev/sdb3.
Based on hints in various articles, it appears that JFS might be able to do Scenario A, but not with Linux; meaning that Scenario B is my only option if I want multiple JFS partitions, each with an external journal. Any confirmation one way or the other?
Second, how big should the journal partition(s) be? My understanding (from Wikipedia - yeah, I know) is that JFS journals are fixed at 32 MB. Should journal partitions be exactly 32 MB, or should I allow some overhead? If Scenario A is viable, should the shared journal be 32 MB (plus overhead), or 32 MB per each "share" (96 MB plus overhead)?
Third, any recommendations/hints/warnings/experiences with JFS that anyone would care to pass on?
Distribution: openSuSE 42.1_64-KDE, Ubuntu 14.04, Mint 17.2
As I understand it, sharing journals wouldn't really make sense, but this is also depending from the type of journaling you want to use. I use ext3 with 400 MB journals per partition and data journaling. You might want to read up the ext3 man and info pages for some background and also