Archive for the ‘Virtualisation’ Category

VMware VMFS Volume Size – Finding the Sweetspot

Reading a knowledge base post on the equallogics site I gleaned the following variables in relation to ESX that will have a factor on deciding VMFS volume size;

  1. ESX has a limit of 64 targets (volumes) per host
    • This is important in a HA / DRS environment where each host in the cluster must have access to all volumes even if the guest is currently running on another host.
    • Hence keeping volume counts down will improve scalability of the cluster
  2. ESX has a maximum queue length per target of 32 IO’s -
    • Thus more volumes means less pausing of IO opperations
  3. Certain Opperations (Start/Stop VM / Snapshot / vMotion) Require exclusive access to volume
    • Thus for a short period of time other vm’s IO is paused -
    • the more VM’s per volume the more this will impact performance
  4. VI 3.5 didn’t support MPIO so more volumes increased throughput
    • Does this matter anymore with MPIO in ESX 4? and multiple sessions per host taking advantage of all paths to the target.
  5. Don’t forget to account for snapshots in your volume size
    • vmware snapshots grow very quickly as they are an on-write copy delta of both the vm memory and it’s virtual hard disk.

ESX & SSH – Enable Remote Login

ESX ships with SSH enabled by default – so it may come as a surprise that it’s not actually possible to login from a remote station out of the box :o┬áTo enable remote logins we need to make a change to the ssh daemon config file, and restart the ssh service.

Why would you want to do this? Well chances are you already use DRAC or iLO for quick access to the service console on your esx box and chances are you’ve already got annoyed by the limited view screen space when comparing vswitch, port group and pnic configs.

#Move Context to the SSH Config Directory
[root@yourbox ]#
cd /etc/ssh

#Make a backup of the config file :)
[root@yourbox ]#cp sshd_config sshd_config.bkup

#Use sed to substitute the config string no with yes
[root@yourbox ]#
sed ‘s/PermitRootLogin no/PermitRootLogin yes/’ sshd_config > sshd_config

#Restart SSH so it picks up the config change
service sshd restart

sed is a very flexible stream editor but I mainly use it for substituting strings; more info on sed can be found on the oracle site

You might want to switch remote logins off when you’re not using SSH.

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