On Wed, Nov 16 at  9:35, David Dyer-Bennet wrote:

On Tue, November 15, 2011 17:05, Anatoly wrote:
Good day,

The speed of send/recv is around 30-60 MBytes/s for initial send and
17-25 MBytes/s for incremental. I have seen lots of setups with 1 disk
to 100+ disks in pool. But the speed doesn't vary in any degree. As I
understand 'zfs send' is a limiting factor. I did tests by sending to
/dev/null. It worked out too slow and absolutely not scalable.
None of cpu/memory/disk activity were in peak load, so there is of room
for improvement.

What you're probably seeing with incremental sends is that the disks being
read are hitting their IOPS limits.  Zfs send does random reads all over
the place -- every block that's changed since the last incremental send is
read, in TXG order.  So that's essentially random reads all of the disk.

Anatoly didn't state whether his 160GB file test was done on a virgin
pool, or whether it was allocated out of an existing pool.  If the
latter, your comment is the likely explanation.  If the former, your
comment wouldn't explain the slow performance.


Eric D. Mudama

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