On 29-Dec-09, at 11:53 PM, Ross Walker wrote:
On Dec 29, 2009, at 12:36 PM, Bob Friesenhahn
<bfrie...@simple.dallas.tx.us> wrote:
...
However, zfs does not implement "RAID 1" either. This is easily
demonstrated since you can unplug one side of the mirror and the
writes to the zfs mirror will still succeed, catching up the
mirror which is behind as soon as it is plugged back in. When
using mirrors, zfs supports logic which will catch that mirror
back up (only sending the missing updates) when connectivity
improves. With RAID 1 where is no way to recover a mirror other
than a full copy from the other drive.
That's not completely true these days as a lot of raid
implementations use bitmaps to track changed blocks and a raid1
continues to function when the other side disappears. The real
difference is the mirror implementation in ZFS is in the file
system and not at an abstracted block-io layer so it is more
intelligent in it's use and layout.
Another important difference is that ZFS has the means to know which
side of a mirror returned valid data.
--Toby
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