Robert Chen wrote: > question is ZFS uses COW(copy on write), does this mean it will > double usage of capacity or waste the capacity? > > What COW really do? No mirror also has COW? > > Please help me, thanks. > > Robert > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss >
It doesn't. Page 11 of the following slides illustrates how COW works in ZFS: http://www.opensolaris.org/os/community/zfs/docs/zfs_last.pdf "Blocks containing active data are never overwritten in place; instead, a new block is allocated, modified data is written to it, and then any metadata blocks referencing it are similarly read, reallocated, and written. To reduce the overhead of this process, multiple updates are grouped into transaction groups, and an intent log is used when synchronous write semantics are required."(from http://en.wikipedia.org/wiki/ZFS) IN snapshot scenario, COW consumes much less disk space and is much faster. Raymond _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
