2012-05-03 3:07, Fred Liu wrote:
There is no specific problem to resolve. Just want to get sort of accurate equation between the "raw storage size" and the "usable storage size" although the *meta file* size is trivial. If you do mass storage budget, this equation is meaningful.
I don't think "accurate equations" are applicable in this case. You can have estimates like "no more/no less than X" based on, basically, level of redundancy and its overhead. ZFS metadata overhead can also be smaller or bigger, depending on your data's typical block size (fixed for zvols at creation time, variable for files); i.e. if your data is expected to be in very small pieces (comparable to single sector size), you'd have big overhead due to required redundancy and metadata. For data in large chunks overheads would be smaller. This gives you something like "available space won't be smaller than M disks from my M+N redundant raidzN arrays minus O percent for metadata." You can also constrain these estimates' range by other assumptions like expected dedup or compression ratios, and hope that your end-users would be able to stuff even more of their addressable data into the pool (because it would be sparse, compressable, and/or not unique), but in the end that's unpredictable from the start. HTH, //Jim _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
