Steve:

What is the latency on your intersite connection?

Best regards,

Mike, x7942
RMD IT Client Services

On Thu, Oct 30, 2014 at 8:35 AM, Steven Harris <steve AT stevenharris DOT info>
wrote:

> Hi All
>
> I have a TSM 6.3.4 server on newish P7 hardware and AIX V7.1. HBAs are
> all 8Gb.  The sans behind it are 8Gb or 4Gb depending which path they
> take as we are in the middle of a SAN upgrade and there is still an old
> switch in the mix.
>
> Disk is XIV behind SVC.  Tape is TS3500 and LTO5.
>
> According to the LTO wikipedia entry I should be able to get 140MB/sec
> raw out of the drive.  I have an internal company document that suggests
> sustained 210MB/sec (compressed) is attainable in the real world.
>
> So far my server backs up 500GB per night of DB2 and Oracle databases on
> to file pools, without deduplication.  Housekeeping then does a
> single-streamed simultaneous migrate and copy to onsite and offsite
> tapes.  Inter site bandwidth is 4Gb and I have most of that to myself.
>
> That process takes over 5 hours so I'm seeing less than 100MB/sec.
>
> Accordingly I started a tuning exercise.  I copied 50GB of my filepool
> twice to give me a test dataset and started testing, of course when
> there was no other activity on the TSM box.
>
> The data comes off disk at 500MB/sec to /dev/null, so that is not a
> bottleneck.
>
> Copying using dd to tape runs at a peak of 120MB/sec with periods of
> much lower than that, as measured using nmon's fc stats on the HBAs. I
> presume some of that slowdown is where the tape reaches its end and has
> to reverse direction.
>
> Elapsed time for 100GB is 18 min, with little variation so average speed
> is 95MB/sec
>
> dd ibs and obs values were varied and ibs=256K obs=1024K seems to give
> the best result.
>
> Elapsed time is very consistent.
>
> Copying to a local drive on the same switch blade as the tape HBA or
> copying across blades made no difference.
>
> Copying to a drive at the remote site increased elapsed time by 2
> minutes, as one would expect with more switches in the path and a longer
> turnaround time.
>
> Tape to tape copy was not noticeably different to disk to tape.
>
> Reading from tape to /dev/null was no different.
>
> In all cases CPU time was about half of the elapsed time.
>
> lsattr on the drives shows that compression is on (this is also the
> default)
>
> The tape FC adapters are set to use the large transfer size.
>
> The test was also run using 64KB pages and svmon was used to verify the
> setting was effective. Again no difference.
>
> I'm running out of ideas here.  num_cmd_elements on the hbas is 500 (the
> default)  I'm thinking of increasing that to 2000, but it will require
> an outage and hence change control.
>
> Does anyone have any ideas, references I could look at or practical
> advice as to how to get this to perform?
>
> Thanks
>
> Steve
>
> Steven Harris
> TSM Admin
> Canberra Australia
>