illumos gate

In the spirit of having additional options, perhaps it is time to explore the possibility of implementing other adaptive cache algorithms besides ARC for ZFS.

• Dueling Clock (http://www.date-conference.com/proceedings/PAPERS/2010/DATE10/PDFFILES/07.7_2.PDF)
• CAR (http://www-cs.stanford.edu/~sbansal/pubs/fast04.pdf)
• DSB (http://www.jilp.org/jwac-1/online/papers/005_gao.pdf)
• LIRS (http://en.wikipedia.org/wiki/LIRS_caching_algorithm)

would be beneficial to have as block cache for ZFS as an alternative to ARC. This is not a slight against ARC, however, this is for the few workloads (or few systems) that ARC is not the optimal solution.

Granted this would a low-priority task, this however gives a few benefits for illumos:

• Move away from a patent-encumbered algorithm (ARC)
• Provide ZFS functionality for systems that were traditionally not optimized for ZFS (i.e low memory systems, OSes with suboptimal memory management like Linux)
• Provide an alternative algorithm to use in the few cases that ARC is not optimized for it
• Give users the freedom to choose.