On Sun, Jun 12, 2011 at 5:28 PM, Nico Williams <n...@cryptonector.com>wrote:
> On Sun, Jun 12, 2011 at 4:14 PM, Scott Lawson > <scott.law...@manukau.ac.nz> wrote: > > I have an interesting question that may or may not be answerable from > some > > internal > > ZFS semantics. > > This is really standard Unix filesystem semantics. > > > [...] > > > > So total storage used is around ~7.5MB due to the hard linking taking > place > > on each store. > > > > If hard linking capability had been turned off, this same message would > have > > used 1500 x 2MB =3GB > > worth of storage. > > > > My question is there any simple ways of determining the space savings on > > each of the stores from the usage of hard links? [...] > > But... you just did! :) It's: number of hard links * (file size + > sum(size of link names and/or directory slot size)). For sufficiently > large files (say, larger than one disk block) you could approximate > that as: number of hard links * file size. The key is the number of > hard links, which will typically vary, but for e-mails that go to all > users, well, you know the number of links then is the number of users. > > You could write a script to do this -- just look at the size and > hard-link count of every file in the store, apply the above formula, > add up the inflated sizes, and you're done. > > Nico > > PS: Is it really the case that Exchange still doesn't deduplicate > e-mails? Really? It's much simpler to implement dedup in a mail > store than in a filesystem... > MS has had SIS since Exchange 4.0. They dumped it in 2010 because it was a huge source of their small random I/O's. In an effort to allow Exchange to be more "storage friendly" (IE: more of a large sequential I/O profile), they've done away with SIS. The defense for it is that you can buy more "cheap" storage for less money than you'd save with SIS and 15k rpm disks. Whether that's factual I suppose is for the reader to decide. --Tim
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