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тАО09-24-2009 02:34 AM
тАО09-24-2009 02:34 AM
Swap is less then memory
please share your understandings
Currently i have 8GB memory and 8 GB swap in one server. What will be the impact if i add 4 GB more memory without adding SWAP due to un availability of physical space on HDD.
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тАО09-24-2009 02:44 AM
тАО09-24-2009 02:44 AM
Re: Swap is less then memory
i will not recommend it.
mikap
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тАО09-24-2009 03:06 AM
тАО09-24-2009 03:06 AM
Re: Swap is less then memory
with the mechanism of pseudo-swap the computation of 1:1 of memory:swap is no longer so restricted.
Currently you can find large systems with 32 Gb and over of memory but not 32 Gb also of swap. Obviously all of it depends on the load of the system and what it has to do. The pseudo-swap mechanism does the computation less restricted as it gives the system something of "virtual" swap calculated like real swap space.
You can see if pseudo-swap is enabled if you have line "memory" in swapinfo -tam.
Definitely I don't see an issue if you have 12 Gb of memory and 8 of swap and pseudo-swap enabled.
Though, fi you want to have anyway some more swap, consider that you can have secondary swap devices on other volume groups or even in other Volume Manager like VxVM. So when you state there's no space on HDD it sounds to me only about vg00.
HTH.
Best regards,
Fabio
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тАО09-24-2009 03:11 AM
тАО09-24-2009 03:11 AM
Re: Swap is less then memory
Swap space does not have to be located on just one disk. You can add additional space on any available lvol with the swapon command. Note that this will be temporary until you add the additional space to fstab. Use swapinfo -tam to see how your RAM is being mapped to the swap areas.
Bill Hassell, sysadmin
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тАО09-24-2009 03:26 AM
тАО09-24-2009 03:26 AM
Re: Swap is less then memory
Thanks for your feedback.
Below is the swapinfo -tam command output.
sr7_pr#swapinfo -tam
Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 8192 18 8174 0% 0 - 1 /dev/vg00/lvol2
reserve - 4095 -4095
memory 8190 2124 6066 26%
total 16382 6237 10145 38% - 0 -
Do we still need to increase SWAP????
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тАО09-24-2009 04:13 AM
тАО09-24-2009 04:13 AM
Re: Swap is less then memory
All is depending upon your system load. if you are going to install some database or SAP then its recomended that swap is double of your Physical Memory.
The bottom line is depending upon your application load swap is required.
Suraj
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тАО09-25-2009 05:28 AM
тАО09-25-2009 05:28 AM
Re: Swap is less then memory
Not yet. You haven't expanded the current applications to use the extra space yet. Since you can add swap at any time without a reboot, I would just monitor things and watch for usage to move up to 80% before adding more swap. And make sure to don't have dbc_max_pct set to the insane default value of 50%. Set it to something like 3-5%.
Bill Hassell, sysadmin
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тАО09-25-2009 07:22 AM
тАО09-25-2009 07:22 AM
Re: Swap is less then memory
Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 8192 18 8174 0% 0 - 1 /dev/vg00/lvol2
reserve - 4095 -4095
memory 8190 2124 6066 26%
total 16382 6237 10145 38% - 0 -
Total swap is only 38%. So I'd add in the 4 GB. Question: Are you running or expect to run Oracle or another application with high requirements of shared memory or SGA?