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Related to this question about using an SSD for system and HDD for data, except I would like my system to do this automatically...

Is it possible to have several layers of storage and push items automatically between them, using preferably free, open-source software?

I know of hugely expensive enterprise-class solutions like the EMC SAN->EMC Centera automatic archiving, but I was wondering if this sort of staged storage is possible to do automatically.

It would be nice to be able to have several layers in this : Memory->SSD->HDD->slower HDD or tape or some other archive solution.

Are there any filesystems which can do this automatically? (ZFS, Btrfs, HAMMER?)

Any Unix-variants are fine, as I'm interested in how this works and whether it's likely to be portable to Linux or other flavours (BSD etc).

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Well, ZFS uses a storage layering called Hybrid Storage Pool (HSP):

  1. Layer: memory
  2. Layer: SSD-based read-caches (L2ARC) and write-caches (separate intent log aka slog).
  3. Layer: (cheap) harddisks

With HSP its easy to automatically benefit from the advantages of SSDs compared to a harddisk-only solution. A system using HSP can be both faster and cheaper than the latter. See this link for some nice examples and more details.

I think there are plans regarding hierarchical storage management (HSM) for ZFS (see for example the Automatic Data Migration (ADM) OpenSolaris project) but I don't know its current status.

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This is just what I was thinking of, thanks! (Now to help on the Linux port... ;) – David Gardner Jul 23 '09 at 8:30
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Answering my own question with something I just found:

I was just updating the kernel and looking at the new stuff that has been added, and there is now a 'CACHEFILES' option which allows for caching (usually remote) filesystems to a local filesystem. I guess I could use this to cache a slower storage mechanism (HDD) to a faster one (SSD), at least for one level of hierarchy.

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Did you try this solution? How does it perform? – skolima Nov 24 '09 at 16:17
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Nevermind - I found out myself that CacheFS for now only supports NFS and AFS. – skolima Nov 24 '09 at 16:22
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Some relevant links. YMMV.

http://code.google.com/p/fscops/ -- "Online Hierarchical Storage Manager (OHSM) is the first attempt towards an enterprise level open source data storage manager which automatically moves data between high-cost and low-cost storage media.".

http://www.tack.ch/unix/dmapi/ -- XFS + DMAPI under Linux

http://jfs.sourceforge.net/ -- JFS + DMAPI under Linux

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The OHSM project looks like an interesting one to follow. Only ext2 and the 2.6.30 kernel is supported for now, but I expect if it works out well then this will gain more filesystems. – David Gardner Jan 22 '10 at 11:41
That project looks abandoned, most recent activity was in 2009. – sendmoreinfo Sep 12 '11 at 22:05
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LVM2 snapshots come to mind... but you can't really do more than a single snapshot.

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SAM-QFS is Sun's existing product and was open-sourced last year. It's CDDL, so you could only directly port it to *BSD.

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