>On Sep 30, 2009, at 5:48 AM, Brian Hubbleday wrote: > >> I am looking to use Opensolaris/ZFS to create an iscsi SAN to >> provide storage for a collection of virtual systems and replicate to >> an offiste device. >> >> While testing the environment I was surprised to see the size of the >> incremental snapshots, which I need to send/receive over a WAN >> connection, considering this is supposed to be block level >> replication. Having run several tests making minor changes to large >> files, I now see what is happening. When I use a text editor to >> modify a file, the whole file is written back to disk and so the >> snapshot includes every written block, whether that block contains >> the same information as before or not. > >Yep, that is how most text editors work.
And dedup will not help you in that case either; unless you append to the end or when you insert a 128K block in the middle of the file, the blocks themselves will all be different. >> Would it be possible to develop the incremental snapshot process so >> that they only contain changed written blocks rather than every >> written block. Certainly in my environment where we have large files >> (>500mb), the effect upon what is sent over the WAN would be >> drastically reduced. > >That is how snapshots work. But your application (text editor) writes >new data. >Maybe you can find another way to edit the files. What type of changes are being made? Casper _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
