Socket or DIsk performance

[Michael Steele_2]

"/dev/vx/dsk/app1dg/app1vol02".

This is for VXVM not an LVM logical volume

[MohitAnchlia]

Then how can I measure the performance for VXVM. Could somebody help me understand how can I see how disks are performing for VxVM. Looks previous examples are applicable to LVM.

[Michael Steele_2]

I'll give you some information on VXVM opposites numbers from the LVM command set. Here's a great URL:

http://www.bhami.com/rosetta.html

pvdisplay vxdisk list
vgdisplay vxdg list / vxprint

[MohitAnchlia]

So I finally found a way using "vxdisk list" to get the device names for the volume. Then ran grep from sar data. I do see devices for that having more avwait than avserv. I am not sure what to do next. How can I tell what needs to be tuned ?

Snap shot of sar (I've cut the device name)
--
device %busy avque r+w/s blks/s avwait avserv

d0 59.69 44.89 515 4094 38.55 3.46
d1 59.24 42.16 507 3990 36.60 3.43
d2 59.86 40.40 509 4014 34.65 3.44
d3 59.43 41.09 509 4029 35.16 3.45
d4 60.90 44.55 517 4126 37.97 3.50
d5 60.74 40.59 507 3984 34.69 3.50
d6 59.01 43.72 513 4117 36.65 3.46
--

[Michael Steele_2]

Finding a disk bottleneck is not as clear cut in VXVM as it is in LVM. You have to go through the /etc/pat_to_inst file. Here's a Solaris disk bottleneck doc that refers to disk suite and metastat. It's related to your situation because of /etc/path_to_inst is involved and because slices are used instead of logical volumes.

Paste in your vxdisk list and vxprint data if you can't get what you need.

[MohitAnchlia]

Attached document tells how to identify associated file system. I already know which file system these disks point to. I am trying to understand how much of a problem it is and how it can be tuned.

[Michael Steele_2]

Oh, well, in that case you have a number of options beginning with your hardware and raid level. If this is a raid 5 consider mirroring only or stripping and mirroring, raids 0, 1, or 01 or 10. Raids 01 and 10 will be striped out in disk groups and disk groups can be tricky when one disk in the group fails. Depends on the type of disk array that you have.

Check the rotation speed on your disks and consider getting faster disks.

From a O/S level consider additional file system on additional disk to load balance better. This is probably your best choice.

But reviewing your sar -d report all of your avwait times are 10 times greater than avserv times. This is a significant bottleneck.

I'd throw more disks at the problem. Usually adding in more spindles is what Oracle and other databases will also recommend.

Consult your dba's for advice on what the database and application recommend for optimal performance and compatiabilty. For example, they may not be able to handle a new file system well. Especailly if code changes are involved.

[MohitAnchlia]

One thing I don't understand is that when writing files it's fast. But, while moving files it slows down. What could be the theory ? Is there a way to balance I/O within existing resources.

[Michael Steele_2]

If you are using online JFS then you can defrag your file systems to increase performance.

To test for online JFS try

fsadm -F vxfs -D -E /filesystem

What does this return?

[MohitAnchlia]

I don't even see -D as an option.

This is what I get for fsadm -h:

usage: fsadm [-F FStype] [-V] [-o specific_options] special