[Veritas-vx] Relayout volume from 2 to 4 columns

Wed Jan 6 11:28:11 CST 2010

Striping across Enterprise LUNs allows you to use more SCSI queues/transaction, and follow the template of setting the number of read/write threads to the number of stripe cols, and have it work efficiently, amongst other arguments for the config.

Not everyone needs this configuration, but it's the difference between made and missed SLAs for a lot of configurations.

Cheers,

Jf

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From: veritas-vx-bounces at mailman.eng.auburn.edu <veritas-vx-bounces at mailman.eng.auburn.edu> 
To: veritas-vx at mailman.eng.auburn.edu <veritas-vx at mailman.eng.auburn.edu> 
Sent: Wed Jan 06 10:19:56 2010
Subject: Re: [Veritas-vx] Relayout volume from 2 to 4 columns 

>the ISP feature of VM would allow you to drill down to individual spindles and place subdisks on each spindle.

Individual spindles of the RAID group? Doesn't that defeat the purpose of the RAID group?
Striping across LUNs gets ...interesting; we usually just use them concat. Of course that's with a real SAN array such as Hitachi 99x0 or Sun 61x0.
I'm not sure I see the point of striping LUNs. If you are having performance problems from the array, fix the layout of the RAID group on the array: that's why you pay the big bucks to Hitachi for their hardware. I not sure I want to know about the load that could flatline a RAID-6 array of 6 15K RPM Fiber channel disks backed by a multigigabyte RAM cache.

I have certainly seen bad storage layout on the host cause hot spots. That's when people make ridiculous numbers of small (gigabyte or so) volumes scattered all over the place -- another argument against the old way of doing things with databases and raw volumes (if you're going to use raw volumes at least use decent size ones not 2GB each ). While old (< 10) Solaris AIO did indeed suck dead bunnies thorugh a straw for performance, that's no longer a problem in Solaris 10 ZFS if you use it natively (using "branded" zones to run Solaris 8 and 9 puts the old AIO interface in front) nor would I expect it to be a problem with VxFS.

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	From: veritas-vx-bounces at mailman.eng.auburn.edu [mailto:veritas-vx-bounces at mailman.eng.auburn.edu] On Behalf Of William Havey
	Sent: Wednesday, January 06, 2010 12:00 PM
	To: przemolicc at poczta.fm
	Cc: veritas-vx at mailman.eng.auburn.edu
	Subject: Re: [Veritas-vx] Relayout volume from 2 to 4 columns

	VM views the two raid groups as single LUNs. It needn't be concerned with the layout of each raid group. To change from 2 columns to 4 columns use the relayout option to vxassist and also specify the two new LUNs on which to place the two new columns.

	That being said, the ISP feature of VM would allow you to drill down to individual spindles and place subdisks on each spindle.

	Bill

	On Wed, Jan 6, 2010 at 6:36 AM, <przemolicc at poczta.fm> wrote:

		Hello,

		we are using VSF 5.0 MP3 on Solaris 10 attached to SAN-based hardware array.
		On this array we have created 2 raid groups and on each RG we have created
		a few LUNs:

		raid group:   RG1    RG2
		             LUN1   LUN7
		             LUN2   LUN8
		             LUN3   LUN9
		             LUN4   LUN10
		             LUN5   LUN11
		             LUN6   LUN12

		For performance reason some of our volumes are striped between the two raid groups
		(using two columns ncol=2) e.g.:

		pl <name> <vol> ENABLED ACTIVE 419256320 STRIPE 2/128 RW

		In this configuration IOs involves two raid groups.

		It seems that in the future in certain cases performance might be not as expected
		so we would like to add two additional LUNs (taken from two additional raid groups)
		and relayout the whole volume from 2-col to 4-cols e.g.:

		raid group:   RG1    RG2    RG3    RG4
		             LUN1   LUN7   LUN13  LUN19
		             LUN2   LUN8   LUN14  LUN20
		             LUN3   LUN9   LUN15  LUN21
		             LUN4   LUN10  LUN16  LUN22
		             LUN5   LUN11  LUN17  LUN23
		             LUN6   LUN12  LUN18  LUN24

		Is it possible to order relayout of existings volumes to spread it over all four
		RGs ? Can I point somehow that it should relayout using these particular LUNs ?

		Regards
		Przemyslaw Bak (przemol)
		--
		http://przemol.blogspot.com/

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