On Oct 2, 2009, at 11:54 AM, Robert Milkowski wrote: > Stuart Anderson wrote: >> >> On Oct 2, 2009, at 5:05 AM, Robert Milkowski wrote: >> >>> Stuart Anderson wrote: >>>> I am wondering if the following idea makes any sense as a way to get ZFS >>>> to cache compressed data in DRAM? >>>> >>>> In particular, given a 2-way zvol mirror of highly compressible data on >>>> persistent storage devices, what would go wrong if I dynamically added a >>>> ramdisk as a 3rd mirror device at boot time? >>>> >>>> Would ZFS route most (or all) of the reads to the lower latency DRAM >>>> device? >>>> >>>> In the case of an un-clean shutdown where there was no opportunity to >>>> actively remove the ramdisk from the pool before shutdown would there be >>>> any problem at boot time when the ramdisk is still registered but >>>> unavailable? >>>> >>>> Note, this Gedanken experiment is for highly compressible (~9x) metadata >>>> for a non-ZFS filesystem. >>>> >>> You would only get about 33% of IO's served from ram-disk. >> >> With SVM you are allowed to specify a read policy on sub-mirrors for just >> this reason, e.g., >> http://wikis.sun.com/display/BigAdmin/Using+a+SVM+submirror+on+a+ramdisk+to+increase+read+performance >> >> >> Is there no equivalent in ZFS? >> > > Nope, at least not right now.
Curious if anyone knows of any other ideas/plans for ZFS caching compressed data internally? or externally via a ramdisk mirror device that handles most/all read requests? Thanks. -- Stuart Anderson ander...@ligo.caltech.edu http://www.ligo.caltech.edu/~anderson _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
