[clug] Advice: Overlay mounts or LVM tweaking for dual-media storage?

steve jenkin sjenkin at canb.auug.org.au
Sat Nov 19 01:22:51 MST 2011


I want to play with an idea and so this question before I try in earnest :-)

I'd like to setup a desktop with "dual media" - two disks of different
sizes and capabilities.

The 'small fast' disk to be used both as a cache and as primary storage
for new or modified files.

The 'big slow' disk to be used for files that are a) securely backed up
elsewhere and b) are low-frequency use.

As files are backed up from the small-fast disk, they are to be copied
to the big-slow-disk and deleted from the s-f-d unless tagged as 'keep
in cache' (hmmmm. not sure just yet how to do that!)

-------------------------------------------------------

So how do I implement this to be transparent to the O/S and user?

 I know I could use an 'overlay' or transparent mount of the big-slow
disk onto the small-fast disk and have the backup process migrate files
between the two disks. Have fought with the daemon a few years back and
I hope things have improved - like being more broadly supported in
kernels. [IIRC, there were a couple of different implementations.]

I don't know enough about the caching filesystem, if it can be tweaked
in this way or not. Have never used it, but heard it mentioned.
Sorta the solution I want if it does this sort of thing.

Or is there some magic I can do with LVM?
Like RAID-0, stripe the two disks and somehow copy data blocks from
small-fast to big-slow.
[But I don't like it because there is only a single filesystem and one
set of inodes. Recoverability in event of disk-fail is an issue]

Or any other cute variations/abuses of LVM that you've seen/used???

Thanks in Advance.

steve j

-- 
Steve Jenkin, Info Tech, Systems and Design Specialist.
0412 786 915 (+61 412 786 915)
PO Box 48, Kippax ACT 2615, AUSTRALIA

sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin


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