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).