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тАО06-02-2005 08:14 PM - last edited on тАО08-24-2014 08:33 PM by Lisa198503
тАО06-02-2005 08:14 PM - last edited on тАО08-24-2014 08:33 PM by Lisa198503
swapspace on dedicated disks?
Current configuration:
Physical memory: 9 Gb
swapspace: 8 Gb on two devices /dev/vg00/lvol2 and /dev/vg00/lvol9
rootdisk (vg00) /dev/dsk/c1t2d0 mirrored on /dev/dsk/c2t2d0
We want to extend memory to the max. (16 Gb)
1. What is a good size for swapspace?
2. Do we get a better performance when swapspace is allocated on dedicated swapdisks?
Thanks for your help!
Ric
P.S. This thread has been moved from HP-UX Technical Documentation to HP-UX > sysadmin. -HP Forum Moderator
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тАО06-02-2005 10:47 PM
тАО06-02-2005 10:47 PM
Re: swapspace on dedicated disks?
You need to allocate swap space but, if you have enough memory, it is not used. And, for performance reason it should not be used.
So, what kind of disk you allocate the swap space on is not important.
It is normal to allocate at least the same swap size as the size of the primary memory. HP-UX reserves swap for all processes and, if there is less swap then primary memory you may get errors as "cannot reserve swap" or similar.
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тАО06-02-2005 10:47 PM
тАО06-02-2005 10:47 PM
Re: swapspace on dedicated disks?
(2) SURE, if you can afford it, but if you aren't swapping, then it can be a waste of resources.
live free or die
harry d brown jr
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тАО06-02-2005 11:30 PM
тАО06-02-2005 11:30 PM
Re: swapspace on dedicated disks?
Mark Syder (like the drink but spelt different)
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тАО06-03-2005 12:51 AM
тАО06-03-2005 12:51 AM
Re: swapspace on dedicated disks?
Dave
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тАО06-03-2005 01:02 AM
тАО06-03-2005 01:02 AM
Re: swapspace on dedicated disks?
You can safely leave the swap space alone. As long as you are not actually paging and your allocation of swap is low, the additional disk space may not be needed. To be sure, take a look at swapinfo -tam
So long as there is plenty of unallocated swap during peak operations, you will be fine. If you are concerned, you may want to add a secondary swap area of lower priority.
2. There are a number of theories on this. Many say don't mirror swap. I generally deal with systems that have two local disks. Therefore I have no choice but to put swap on the same local disk that I boot off of, which is mirrored.
If you have lots of disks, having several smaller swap areas with different priority may give better swap performance. Again, if you are not actually paging, the layout won't make a difference.
In an ideal world I like a small, minimal swap area as highest priority, normally the minimum half of physical ram. If I have any supplemental swap areas, they are bigger, ideally on their own disk and set to a higher priority number, therefore lower priority for use. That way they don't get used.
I've never had a chance top create my ideal swap layout, working with rp servers the way I have.
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тАО06-03-2005 02:23 AM
тАО06-03-2005 02:23 AM
Re: swapspace on dedicated disks?
2) It's pointless to combine performance and swap in the same sentence because once swapping starts to any significant degree, it really doesn't matter. My standard response for modern boxes is that "worrying about swap layout is akin to rearranging the deck chairs on the Titanic".
3) Although you didn't ask, swap space should have absolutely nothing to do with dump space --- they serve entirely different purposes. Moreover, all swap space should always be mirrored and dump space should never be mirrored.