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08-21-2012 03:00 AM
08-21-2012 03:00 AM
Disks acting a very slowly through the fibre channel on HP-UX 11i v3
Hello
When we doing a simple test like "timex dd if=/dev/zero ..." we gets speed ~130MBps. But having the same equipment (other blades) on Linux we can get 500~600MBps. Please help us find out where is the bottleneck.
Some info here:
HP 451871-B21 8Gb Dual Port PCIe Fibre Channel Mezzanine
HP-UX testmach B.11.31 U ia64
Driver Version = @(#) fcd B.11.31.1109 May 23 2011
patchinfo? other information?
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08-21-2012 03:30 AM
08-21-2012 03:30 AM
Re: Disks acting a very slowly through the fibre channel on HP-UX 11i v3
What kind of device is the target and check if you use by chance the "standby" path?
Hope this helps!
Regards
Torsten.
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08-21-2012 04:51 AM
08-21-2012 04:51 AM
Re: Disks acting a very slowly through the fibre channel on HP-UX 11i v3
As Torsten said, you need to tell us what sort of disk array you are talking to here.. there are many variables that could make a significant difference to why Linux appears faster - top of my list for something as straightforward as a sequential IO operation like a dd would be
i) block sizes (influenced by the filesystem - although you don't indicate whether you were doing the dd to a filesystem, to the block device, or to the raw device?)
ii) disk SCSI queue depths - I don't know what the default is on Linux, but it may be deeper than the default of 8 on HP-UX - this is a farirly in-depth topic - see this whitepaper for details: http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c02054623/c02054623.pdf
iii) MPIO settings - the default of round-robin on HP-UX is not great for sequential IO with many disk arrays - again you'd have to tell me what Linux is set to for comparison... for example on XP disk arrays for sequential IO, I have often found weighted_rr with a wrr_path_weight of about 1000 per LUNpath works much better
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08-21-2012 05:25 AM
08-21-2012 05:25 AM
Re: Disks acting a very slowly through the fibre channel on HP-UX 11i v3
On other side of fibre channel we have SAN switch connected to 3PAR disk array.
i) i have mounted test block device 10G with vxfs file system to perform dd
The full string look like to
timex dd if=/dev/zero of=/test_ssd/file count=8192k bs=1024
ii) depth is really 8 there (we didn't change standart value). I will change and test. Thanks
iii) Usally to avoid multipath influence i gave only one path from 3par storage.
PS: After deleting stale devices from system the speed slumped to 40MBps.
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08-21-2012 06:27 AM - edited 08-21-2012 06:28 AM
08-21-2012 06:27 AM - edited 08-21-2012 06:28 AM
Re: Disks acting a very slowly through the fibre channel on HP-UX 11i v3
bs could be larger.
The server has 8Gb, the array port probably only 4Gb. Using multipath would be better - check also if the host mode is set to hpux on the array.
Consider a bad connection/cable also.
Hope this helps!
Regards
Torsten.
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08-21-2012 06:53 AM
08-21-2012 06:53 AM
Re: Disks acting a very slowly through the fibre channel on HP-UX 11i v3
iii) Usally to avoid multipath influence i gave only one path from 3par storage
You may still be doing multi-pathing... by default if you use a legacy DSF on HP-UX11.31 (i.e. /dev/rdsk rather than /dev/rdisk), you will still be doing multi-pathing... see the attribute leg_mpath_enable in the scsimgr(1m) man page
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