AIX ramdisks

Long ago (think 1999ish), I wrote a techdoc on how to put JFS on a ramdisk on AIX. We called them FAXES, because we would fax them to people, and this was before FAQ was a common acronym. At some point, I put it into the TechDoc system when that came out, because there was a push to use the system.

I lost the original text, but the techdoc lived on. It was rewritten after I left big blue. You can see their better version here:

I don’t want to copy their doc, because they can be testy about such things. Heck, they can be testy when they plagiarize my docs. The key reference is syntax, which I’ll summarize here. You can also just look up the manpages on mkramdisk, mkfs,

Make a pinned-memory ramdisk: mkramdisk $bytes
The default uses pinend RAM, which is required for JFS or JFS2.

Make an un-pinned ramdisk: mkramdisk -u $bytes
This is okay for raw devices, maybe UDFS, but not for JFS. There are latency/access requirements on JFS, but at least mkfs knows to throw an error here if you try to skip it.

When you run mkfs on /dev/ramdisk0 as JFS, it’s normal, except you mount -o nointegrity.

When you run mkfs on /dev/ramdisk0 as JFS2, use -o log=INLINE on the format, and the mount.

You can, of course, format UDF as well: udfcreate -f3 -d/dev/ramdisk0 ; mount -vudfs /dev/ramdisk0 /RAMDISK

You could probably run a mksysb to the ramdisk. I don’t know if it would be raw, or if it would be UDFS. That might be useful for high speed testing, but of course, the ramdisk evaporates on reboot. You could dd the ramdisk out to some other media.

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