On 2010-Oct-20 08:36:30 +0800, Never Best <qui...@hotmail.com> wrote: >Sorry I couldn't find this anywhere yet. For deduping it is best to >have the lookup table in RAM, but I wasn't too sure how much RAM is >suggested?
*Lots* >::Assuming 128KB Block Sizes, and 100% unique data: >1TB*1024*1024*1024/128 = 8388608 Blocks >::Each Block needs 8 byte pointer? >8388608*8 = 67108864 bytes >::Ram suggest per TB >67108864/1024/1024 = 64MB > >So if I understand correctly we should have a min of 64MB RAM per TB >for deduping? *hopes my math wasn't way off*, or is there significant >extra overhead stored per block for the lookup table? The rule-of-thumb is 270 bytes per DDT entry - that means a minimum of 2.2GB of RAM (or fast L2ARC) per TB. And note that 128KB is the maximum blocksize - it's quite likely that you will have smaller blocks (which implies more RAM). I know my average blocksize is only a few KB. -- Peter Jeremy
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