Backing up to an external FAT32 disk

[Liam Proven]

I am trying to backup a 98% full RAID array (some 100GB of stuff) onto
a 400GB FAT32 USB2 external hard drive. I don't have space on the RAID
itself to create the archive, nor on my 3G root FS.

I tried (in my /media directory, the mountpoint for both the RAID and
the USB drive):

tar -cvf usbdrive/raid.tar raid/

This worked but I forgot one detail. FAT32 has a max file size of
about 4G. So when the archive got to 4G, it barfed.

I see there are relevant switches: -F parameter change tapes, -L to
split at a certain size, -M for a multivolume archive, but I don't
know how to put these together correctly. Can GNU tar do this? Create
a backup in lots of (/n/ gig) chunks in such a form that it can still
be directly restores? Ideally, compressing them on the way!

Friends have suggested using tar with -FL and a call to mktemp to
split the archive into randomly-named 4G chunks, but then I can't see
how I'd restore it again; how will tar work out what the next volume
to examine is?

Another friend pointed at a discussion here:

http://groups.google.com/group/comp.os.linux.misc/msg/a77a8b76bc08d30a?dmode=source&hl=en

But that needs some manual cleaning up afterwards (so it's not
suitable for, say, scheduling with cron) and I don't follow what the
subscript does.

My external drive is FAT32 so that I can write to it from Windows and
Mac OS X as well as Linux - this is a priority.

I am slightly surprised that I've not been able to find a ready-rolled
solution. I would have thought this was a common requirement! Large
external USB2 or Firewire drives are a popular backup medium in SOHO
environments these days, as tape drives to handle the capacity of
modern hard disks are so expensive they are an enterprise-only
solution. Often the drives come formatted to FAT, as do Flash thumb
drives, because /everything/ can read & write to FAT.

I'm not wedded to using tar - I'd consider dump or something as well.

-- 
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