On Tue, November 15, 2011 20:08, Edward Ned Harvey wrote:
>> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
>> boun...@opensolaris.org] On Behalf Of Anatoly
>> 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
> I suggest watching zpool iostat before, during, and after the send to
> /dev/null. Actually, I take that back - zpool iostat seems to measure
> virtual IOPS, as I just did this on my laptop a minute ago, I saw 1.2k
> which is at least 5-6x higher than my hard drive can handle, which can
> mean it's reading a lot of previously aggregated small blocks from disk,
> which are now sequentially organized on disk. How do you measure physical
> iops? Is it just regular iostat? I have seriously put zero effort into
> answering this question (sorry.)
> I have certainly noticed a delay in the beginning, while the system thinks
> about stuff for a little while to kick off an incremental... And it's
> acknowledged and normal that incrementals are likely fragmented all over
> place so you could be IOPS limited (hence watching the iostat).
> Also, whenever I sit and watch it for long times, I see that it varies
> enormously. For 5 minutes it will be (some speed), and for 5 minutes it
> will be 5x higher...
> Whatever it is, it's something we likely are all seeing, but probably just
> ignoring. If you can find it in your heart to just ignore it too, then
> great, no problem. ;-) Otherwise, it's a matter of digging in and
> characterizing to learn more about it.
I see rather variable io stats while sending incremental backups. The
receiver is a USB disk, so fairly slow, but I get 30MB/s in a good
stretch. I'm compressing the ZFS filesystem on the receiving end, but
much of my content is already-compressed photo files, so it doesn't make a
huge difference. Helps some, though, and at 30MB/s there's no shortage
of CPU horsepower to handle the compression.
The raw files are around 12MB each, probably not fragmented much (they're
just copied over from memory cards). For a small number of the files,
there's a photoshop file that's much bigger (sometimes more than 1GB, if
it's a stitched panorama with layers of changes). And then there are
sidecar XMP files, mostly two per image, and for most of them
web-resolution images, 100kB.
David Dyer-Bennet, d...@dd-b.net; http://dd-b.net/
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