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Excellent! I was just investigating btrfs[0] and realized that it doesn't offer anything like ZFS's "2nd level storage" (L2ARC) which is doing precisely this:
by hf 12y ago
Excellent! I was just investigating btrfs[0] and
realized that it doesn't offer anything like ZFS's
"2nd level storage" (L2ARC) which is doing
precisely this: keep what is nowadays referred to
as hot data on dedicated (read: solid state)
storage; as much as possible.
In the course of this little recherché I hit upon
bcache and dm-cache but found (Debian) user-land
to be entirely lacking (`modprobe dm-cache`
doesn't raise an eyebrow, though).
Having dm-cache support in LVM -- one of those
projects that figure centrally in my personal
sysadmin lore -- would be just heavenly.
[0] Balanced Tree FS. Similar in outlook and approach
to SUN-now-Oracle's
ZFS and -- oh, irony of ironies -- also under the Oracle umbrela.
- koverstreet 12y agoAnnoying thing about have a filesystem and a separate block layer cache (bcache or dm-cache) is they're duplicating a lot of the same work - filesystem maps from inode:offset to physical offset, cache does the same thing. Both doing their own allocation/reclamation/etc. I've been turning bcache into a full blown filesystem in my spare time. It's working now - it's fast, and the code is _small_ compared to other filesystems. Not production ready yet and it'll be awhile before I freeze the on disk format, though.