[EMAIL PROTECTED] wrote:
On Fri, Jul 07, 2006 at 11:59:29AM +0800, Raymond Xiong wrote:
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.
It says also that updating uberblock is an atomic operations. How is it
achieved ?
przemol
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The email thread and document below gives you information about that:
http://www.opensolaris.org/jive/thread.jspa?messageID=19264䭀
http://www.opensolaris.org/os/community/zfs/docs/ondiskformatfinal.pdf
Francois.
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