On Fri, Jun 04, 2010 at 01:03:32PM -0700, Brandon High wrote: > On Fri, Jun 4, 2010 at 12:37 PM, Ray Van Dolson <rvandol...@esri.com> wrote: > > Makes sense. So, as someone else suggested, decreasing my block size > > may improve the deduplication ratio. > > It might. It might make your performance tank, too. > > Decreasing the block size increases the size of the dedup table (DDT). > Every entry in the DDT uses somewhere around 250-270 bytes. If the DDT > gets too large to fit in memory, it will have to be read from disk, > which will destroy any sort of write performance (although a L2ARC on > SSD can help) > > If you move to 64k blocks, you'll double the DDT size and may not > actually increase your ratio. Moving to 8k blocks will increase your > DDT by a factor of 16, and still may not help. > > Changing the recordsize will not affect files that are already in the > dataset. You'll have to recopy them to re-write with the smaller block > size. > > -B
Gotcha. Just trying to make sure I understand how all this works, and if I _would_ in fact see an improvement in dedupe-ratio by tweaking the recordsize with our data-set. Once we know that we can decide if it's worth the extra costs in RAM/L2ARC. Thanks all. Ray _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
