On Wed, Feb 20, 2013 at 5:46 PM, Bob Friesenhahn <
> On Thu, 21 Feb 2013, Sašo Kiselkov wrote:
> On 02/21/2013 12:27 AM, Peter Wood wrote:
>>> Will adding another vdev hurt the performance?
>> In general, the answer is: no. ZFS will try to balance writes to
>> top-level vdevs in a fashion that assures even data distribution. If
>> your data is equally likely to be hit in all places, then you will not
>> incur any performance penalties. If, OTOH, newer data is more likely to
>> be hit than old data
>> , then yes, newer data will be served from fewer spindles. In that case
>> it is possible to do a send/receive of the affected datasets into new
>> locations and then renaming them.
> You have this reversed. The older data is served from fewer spindles than
> data written after the new vdev is added. Performance with the newer data
> should be improved.
That depends entirely on how full the pool is when the new vdev is added,
and how frequently the older data changes, snapshots, etc.
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