Author Archives: iwik

Performance impact when using VMware snapshots

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Using vmware and snapshots? You probably know about vmware best practices about snapshots, which includes

  • The maximum supported amount of snapshots in a chain is 32. However, VMware recommends that you use only 2-3 snapshots in a chain.
  • Use no single snapshot for more than 24-72 hours. Snapshots should not be maintained over long periods of time for application or Virtual Machine version control purposes.
  • An excessive number of delta files in a chain (caused by an excessive number of snapshots) or large delta files may cause decreased virtual machine and host performance.
  • Be especially diligent with snapshot use on high-transaction virtual machines such as email and database servers

But what is real performance inpact of snapshot?

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Big XFS filesystem NFS export mount fails with stale nfs handle

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If you have big XFS filesystem (with lot of files) and you use inode64 mount option, exporting this file system using NFS may fail when mouting this export on client:

Stale NFS file handle

This error is strange and confusing. Workaround is to specify fsid in /etc/exports for this filesystem.

For more information check this nice blog article https://hpc.uni.lu/blog/2014/xfs-and-inode64/

Snapshoting virtual machine running mysql database

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Backup in virtualized enviroment is mostly based on snapshoting entire virtual machine and saving this state to backup repository. This snapshot does not include memory of virtual machine. When you restore virtual machine from this snapshot filesystem is in unclean state, but journal filesystem can handle this. From mysql point of view server crash happended and database can be corrupted and unrecoverable, depending on what queries where running during snapshot. This unpredicted and unconsistent state you don’t want to have as a backup of your data. Continue reading →