How to: Check and change the ESX Swap Partition
An interesting problem occurred the other day with one of our older production ESX 3.0.2 hosts. For the first time with any ESX host we have the service console memory ran out, this resulted in all VM’s becoming unresponsive and loss of service to our users.
Now these hosts were built a couple of years ago by a consultant and all had their service console memory set to the default value of 272MB. I’m in the process of upgrading all hosts to ESX 3.5 U4 and changing the memory levels to the maximum 800MB, this particular host was due to be upgraded in the next 2 weeks. Unfortunate timing!!
VMware support were as helpful as ever and informed my colleague to up the service console memory to 800MB. My only concern was the fact that your swap space is meant to be twice your service console memory. If the memory was only set to 272MB you can be sure that the swap partition wasn’t going to be set to 1600MB.
My colleague was having trouble finding out what size the swap partition was so I gave him a hand. First of all he was doing a df –k at the service console, which shows him the named linux partitions but not the swap partition we were looking for. To get information on all disks and partitions attached to the host we need to run fdisk – l
This command showed us the swap partition created was made up of 1044225 blocks, though we weren’t sure exactly what this equated to in MB.
I took a look at one of our newly built ESX 3.5 U4 hosts and compared it’s fdisk –l results to the scripts used to build it. I quickly found that by dividing by 1024 you could get the size of the partitions. So in this case the swap partition on the ESX 3.0.2 host was roughly 1GB which was less than the recommended 2 x console memory sizing.
On this occasion VMware support advised us that it should be OK as it was. That coupled with the fact we are going to rebuild the server in the coming weeks was enough for us to call the case closed.
However what if we did want to change it? I’d always been taught that changing the swap partition after the host had been built usually meant a full rebuild. However as I’ve been working my way through Scott Lowe’s Mastering Vmware vSphere 4 book I came across the steps to do it without a rebuild. It’s always recommended to rebuild a host as opposed to take this action, however occasionally needs must.
first create a new swap file on an existing service console partition, the command below will create a 1.6GB within the path entered /path/to/
dd if=/dev/zero of=/path/to/swap.file bs=1024 count =1640144
Use the following command to turn this into a usable swap file
mkswap /path/to/swap.file
Now enable the swap file with the following command
swapon /path/to/swap.file
If you do try this, it is entirely at your own risk. I haven’t as I am planning to rebuild in the near future. If I wasn’t I would probably have given this a shot just to put my mind at ease.
