Darren Dunham wrote:
In my experience, we would not normally try to mount two different
copies of the same data at the same time on a single host. To avoid
confusion, we would especially not want to do this if the data represents
two different points of time. I would encourage you to stick with more
traditional, tried, and true disaster recovery methods. Remember: disaster
recovery is almost entirely a process, not technology.
Darn straight.
Of course those administrators keep asking for it anyway. The VxVM list
gets a somewhat consistent stream of requests asking about issues
similar to this.
Think data mining or prod/dev/test environments, I might want to take a
snapshot of my Data with a capital D and perform some set of operations
on it. Of those you have two general use cases:
* A copy of the data set on the same host but used by a different
application. A ZFS snapshot might meet the requirements in some of
those cases. However, in a lot of those cases you're going to want
the copy of the data set on different physical media so as not to
interfere with the performance of your currently in-use application.
* A copy of the dataset on a different host. zfs send/recv might
meet the requirements in some of these cases. However, you may run
into time issues where customers want the snapshot *now* and don't
want to wait for what could be a lengthy send/recv operation.
Since a ZFS pool is, for lack of better terms, the current least common
denominator when it comes to snapshots, host connectivity, and
performance people are going to want to use HW raid arrays and the
snapshot mechanisms.
Oh...and for DR too. One point to choke in a data center so we better
figure that one out too. ;)
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