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swap space size with big memory

hdkid
Occasional Contributor

swap space size with big memory

Dear all!
My boss have bought a Blade server (BL870c i2) and I will install/configure it to virtualize 2 or 3 hosts (they will be oracle servers) on it.

The OS we will use is hp-ux 11.31 VSOE, this system have big memory (64gb), it will be a VM host. So, how swap space is sufficient?

On next month, we will get a big another system (rx8640), it also have 64gb memory, and it will be a data warehouse (Oracle). If as the recommends from manuals, the swap space should be twice memory (128gb), how i will configure it when my hdd is 146gb.

Please give me your recommends, when i'm a new babe with hp-ux, and i have just experience with small systems (for ibm aix, sun solaris, hic :( ).

Thanks in advanced!
7 REPLIES
Dennis Handly
Acclaimed Contributor

Re: swap space size with big memory

>If as the recommends from manuals, the swap space should be twice memory (128gb), how I will configure it when my hdd is 146gb.

This is an outdated recommendation for such large memory machines. If you want performance, you don't want it to use swap and if you have enough RAM, there is no need for so much swap.
GPissutto
Frequent Advisor

Re: swap space size with big memory

In 11iv3 pseudo-swap is enabled by default and it resides in memory. Besides, there is 7/8 of memory should be enough by the book. Some ISVs or development teams require for a rate 1:1, others add 8M or 20GB to it.
hdkid
Occasional Contributor

Re: swap space size with big memory

Thanks Dennis Handly and GPissutto

Do you have a common fomula for sizing the swap space? And how many GB exactly for my case (for both systems: VM host and data warehouse server)?

And the last question: how many gb for the /var volume (for the directory /var/adm/crash)

Before, when my system (both of application and database) on an old rx8620 is crashed, due to the /var volume is too small. So, local HP can't trace the root cause of that issue.

Thanks both very much!
kemo
Trusted Contributor

Re: swap space size with big memory

As a base minimum, it's highly recommended that the swap space should be equal to the amount of physical memory (RAM). Also, it's recommended that the swap space is twice the amount of physical memory (RAM) depending upon the amount of hard disk space available for the system (although this "recommendation" dates back from a time when physical RAM was very expensive and most Unix systems ran with many processes in swap space - a situation that hardly applies in most situations these days, but ancient Unix/Linux myths like this "recommendation" tend to survive well past their "use by" dates). In reality, if you use hibernation you need what was outlined the relevant paragraph above, otherwise you need as much swap space as your system will use - which may be actually be very little in a modern hardware setup. The only downside to having more swap space than you will actually use is the disk space you will be reserving for it.
hvhari
Esteemed Contributor

Re: swap space size with big memory

Swap also serves the purpose for storing the crash dump when system crashes or we take a crash of the system to recover from an un-responsive server. For this purpose we need to keep a decent space reserved. Below documents can give insight to you on how much swap space need to be configured .

http://bizsupport2.austin.hp.com/bc/docs/support/SupportManual/c01914727/c01914727.pdf

http://bizsupport2.austin.hp.com/bc/docs/support/SupportManual/c02465072/c02465072.pdf
Regards,
Hari

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Ken Englander
Regular Advisor

Re: swap space size with big memory

We found it documented and actually it was true that when you are hosting VMs you will need swap space equal to twice the sizes of the VMs you want active simultaneously.
hdkid
Occasional Contributor

Re: swap space size with big memory

Thanks hari/Ken!

@Ken:
What document which show as you said: The swap space will be equal or to twice the VMs simultaneously?