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April 30th, 2013 01:00
Slow speed with one save set writing to tape
We have Networker 7.6 SP4 on Windows 2003 x64 server, 32 GB RAM, 2 Gigabit ehternet cards joined in team and DD670 , 36 GB RAM, Data Domain OS 5.2.2.0-354796. Fujitsu LT60 tape library with 2 tape drives and 24 tape slots. My problem with networker is that it always writes one session with speed which is about one third from total bandwith. That means, if I write 3 save sets(or more, i tried with 4 also) to one tape, then I can get write speed about 100...110 MB/sec. If save sets complete then speed drops accordingly to 60..70 MB/sec with two save sets and 30...40MB/sec with one save set. And that is problem because we have some save sets which are about 2.5TB and it takes about 20h to write it to tape. Its too long. There is no problem, if I clone one save set from DD, because then it gets speed 90..100MB/sec.
I am kind of stuck here, why there is difference between cloning save set from DD and just writing files from DD filesystem. Is there some configurable limit that says 'use only third from bandwith if I write one save set'? I did quick test with three 5GB save sets and another SAN disk and situation seemed about the same. Three save sets was at greater speed and with one save set about the third from total speed.
I tried to find similar situations, read Networker Performance Optimization Planning Guide, installed newest HP LTO Tape drivers, tuned some TCP parameters. But situation stays same. For long term plans I can make proposition to buy more Networker clients so that needed data gets written to DD through Networker and then I can clone it to tape. But it takes time and right now I am trying to find another solution. Any advice, where or what to tune/change so that I can get full speed even when Networker writes only one save set to tape.
ble1
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April 30th, 2013 02:00
The speed you refer to is typical speed you see when client is sending data over routed network with 1Gbps. I would assume your client has 1Gbps network card and connection to storage node goes over switched network.
ble1
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April 30th, 2013 03:00
You get 3rd when network is not optimized. You can try simple test by using the same path with writes outside NW and compare what you get.
sasilik
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April 30th, 2013 03:00
Storage node and client are on the same server which has 2 1GB network cards which are joined with aggregated link. DD has 10GB NIC. Connection from server to DD goes over switched network. Server and Tape library are connected through 4GB fibre.
If Networker writes one save set to the tape then windows task manager shows that one 2Gbps interface has ~16% Network utilization. If Networker writes 3 or more save sets then speed goes up and Network utilization goes up about ~45%. I monitored both NICs in the team and only one NIC was utilized, other got occasional peaks when Networker wrote at speeds 100..110 MB/sec. Is this really 1GB network limitation that it you get only third from bandwith when you have on session between source and target?
sasilik
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April 30th, 2013 05:00
I had same idea just while ago and I must confess that it is sadly so. I copied files to the same server from DD and got similar speed. I guess I must consult with our network admin what we can do about it. At least I have something to point my finger at.
Thierry101
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May 1st, 2013 20:00
your env is similar to ours
"2.5TB and it takes about 20h to write"....how many files and how big each?
sasilik
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May 1st, 2013 23:00
About 1000 files and size is mostly 1...7GB. But does it matter how many files and how big? If I have one session which writes at speed 30...40 MB/sec then it writes ~130GB/hour and ~1.3TB with 10 hour.
Gustavo U
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December 11th, 2013 06:00
Hello!
I'm working with a similar issue, did you find a way to resolve it?
In my case I suppose the problem it's about size (small) and quantity of files.just one save set
Unfortunatelly I can't divide the save set because It's the home folder of users F:\Users,
regards Gustavo U
ble1
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December 11th, 2013 07:00
Performance problems are always cool thing as there are never exactly the same. You may hope that OP found his problem, but statistically chances that this would have same cause as in your case are low. First thing which I see in your email is F:\Users - is this local disk or CIFS share/mount? Also, do not suppose your case might not be driven by file size as small files are typical for user's data (and number of it) so you need to check that too. You can certainly divide that folder by its structure (eg. alphabetically which would give you 26 save sets in worst case scenario).