On Nov 16, 2011, at 7:35 AM, 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.

Not necessarily. I've seen sustained zfs sends in the 600+ MB/sec range
for modest servers. It does depend on how the data is used more than the 
hardware it is stored upon.
 -- richard


ZFS and performance consulting
LISA '11, Boston, MA, December 4-9 

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