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тАО02-26-2002 10:25 AM
тАО02-26-2002 10:25 AM
My question is, do alternate links attached to a tray provide load-balancing or only redundancy? I tried searching through some white papers and there seemed to be hints that the answer is dependant on whether the disk tray in question supports active/active status as opposed to active/passive, but am unsure if this applies to LVM, or VxVM only? Or is some other software required to load-balance?
Solved! Go to Solution.
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тАО02-26-2002 10:31 AM
тАО02-26-2002 10:31 AM
Re: Alternate links on LVM....
With LVM, alternate links do *not* load-balance. The alternate link is used only in the event the primary one fails. Up to seven alternate links are supported by only one can be promoted to a primary upon failure of the primary.
With VxVM, dynamic load-balancing is supported.
Regards!
...JRF...
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тАО02-26-2002 10:34 AM
тАО02-26-2002 10:34 AM
Re: Alternate links on LVM....
I believe VxVM has the capability to do active/active load balancing, but I am unsure whether this is currently supported on HP-UX, although from this manual:
http://docs.hp.com/cgi-bin/fsearch/framedisplay?top=/hpux/onlinedocs/B7961-90025/B7961-90025_top.html&con=/hpux/onlinedocs/B7961-90025/00/00/13-con.html&toc=/hpux/onlinedocs/B7961-90025/00/00/13-toc.html&searchterms=vxvm&queryid=20020226-104003
It seems there is a section on Dynamic Multi Pathing
HTH
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тАО02-26-2002 10:35 AM
тАО02-26-2002 10:35 AM
Solution"vgreduce /dev/dsk/c10/t1/d0 vg02"
the second address becomes the primary. The next step is to vgextend the same disk back
"vgetend /dev/dsk/c10/t1/d0 vg02"
So now the old primary is the backup pvlink. I use this to force single contoler units to use both controlers by doing this to half of the disks. That way there is still redundance if either controler fails but performance is increased if you know where to split the disks.
Obiously on a striped system this is a no-brainer
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тАО02-26-2002 10:43 AM
тАО02-26-2002 10:43 AM
Re: Alternate links on LVM....
Then 5 disks has to be configured through the primary link address and the other 5 disks has to be configured through the alternate link addresses as primary address. In that case the first 5 disk will be accessed by the primary link and the second set of 5 disks will be addressed by the alternate link.
Sandip
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тАО02-26-2002 10:45 AM
тАО02-26-2002 10:45 AM
Re: Alternate links on LVM....
Melvyn, again, correct and with a link, so an 8 for being second with the info.
Mark, I like your poor-man's load-balancing scheme, so you get a 10 for thinking out-of-the-box!
Thanks for the help all of you!
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тАО02-26-2002 10:45 AM
тАО02-26-2002 10:45 AM
Re: Alternate links on LVM....
LVM alternate links only provide redundancy and do not provide any load balancing,
//Quote //
HP-UX does not do load balancing with LVM across pvlinks. LVM will always communicate through the primary path. LVM will only use the alternate path if the primary path becomes unavailable.
VxVM 3.1 will allow load balancing down both paths in what is called active/active mode on the disk. VxVM is available with HP-UX 11i (11.11) only and cannot be used for the root volume group at this release.
Typically, the primary and alternate links are across two different controllers; controller A and controller B. If a disk array had 6 luns, then typically the administrator would set 3 to have primary paths on controller A alternate paths on controller B. The remaining three would be set up with primary paths on controller B and alternate paths on controller A. During normal operation 3 luns would communicate on one controller card and the other 3 using the second controller. The alternate paths would only be used if the primary paths became unavailable for some reason.
//EndQuote//
You can also try the links below for more opinions,
http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x62e65f260cafd4118fef0090279cd0f9,00.html
http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x54d7f841489fd4118fef0090279cd0f9,00.html
Hope this helps.
regds
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тАО02-26-2002 10:54 AM
тАО02-26-2002 10:54 AM
Re: Alternate links on LVM....
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тАО02-27-2002 01:57 AM
тАО02-27-2002 01:57 AM
Re: Alternate links on LVM....
I've monitored this extensively with Glance, and can confirm that the I/O request DEFINITELY follows the new path, as I can see that the I/Os are registered against the "new" device path. In this way, I get to exercise all of the FC cards instead of just half. I cannot provide benchmark results, but batch processing is definitely faster using the PVLINKS.
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тАО04-09-2003 04:25 AM
тАО04-09-2003 04:25 AM
Re: Alternate links on LVM....
Now I have a cluster environment - when i change ag volumegroup on one server and import this volumegroup on the other server - my alternating is gone.
If i want the alternating again on the other server I must activate this vg and run my "alternatescript" - but I din't want to to activate the VG because i will have the package (vg) up and running on the first node.
Have anyone a resolution for this? Mybe I can change the /etc/lvmtab direct?