Software SSD Cache Implementation For Linux?

Annirak writes "With the bottom dropping out of the magnetic disk market and SSD prices still over $3/GB, I want to know if there is a way to to get the best of both worlds. Ideally, a caching algorithm would store frequently used sectors, or sectors used during boot or application launches (hot sectors), to the SSD. Adaptec has a firmware implementation of this concept, called MaxIQ, but this is only for use on their RAID controllers and only works with their special, even more expensive, SSD. Silverstone recently released a device which does this for a single disk, but it is limited: it caches the first part of the magnetic disk, up to the size of the SSD, rather than caching frequently used sectors. The FS-Cache implementation in recent Linux kernels seems to be primarily intended for use in NFS and AFS, without much provision for speeding up local filesystems. Is there a way to use an SSD to act as a hot sector cache for a magnetic disk under Linux?"

Comments

Re:I don't get it

[Penguinisto]

...only if you want to blow out the SSD wear-limits.

What the author wants (I believe) is to have Linux figure down which sectors are read most frequently, and have those mapped/linked/whatever to the SSD for speed reasons.

If that's indeed the case, then why not simply put the MBR, /boot, /bin, and /usr on the SSD, then mount stuff like /home, /tmp, swap, and the like onto a spindle disk? No algorithm needed, thus no overhead needed to run it, etc.