Disk consolidation needed

[tractng]

We have an ongoing issue with a machine for sometimes now.  In the past, Veeam/VMware support would tell us to take a manual snapshot and delete all snapshot when we get this alert.

Do you guys perform this method while the machine is running or shut it down.  I noticed its much faster when the machine was off but last time the support person from VMware had it power on and it took almost a day. 

Besides the speed, the process achieves the same thing?  The machine in question is an Exchange 20120 with 5 disks in a cluster of 2 nodes (it can be set as passive or active).

Thanks,

Tt

[rcporto]

If you can afford the downtime, the preferred/fastest way is with the virtual machine powered off, the reason why you can see here: VMware KB: Delete all Snapshots and Consolidate Snapshots feature FAQ

What is the difference between running the process while the virtual machine is powered on and when it is powered off?

If the virtual machine is running when you click Delete all from the interface or run vmware-cmd <cfg> removesnapshots, an additional snapshot is created to accommodate the incoming I/O while all the other snapshots get committed to the Base Disk. The size of the snapshot can grow depending on the I/O activity. It is ideal to reduce the I/O activity to facilitate the process.

That last snapshot will commit to the Base Disk at the very end of the process. After this, all the snapshot files are deleted.

Note: If the virtual machine is powered off, no additional free space is required and the process will complete faster as there is no need track writes and the additional snapshot and delta file are not created as part of the process.

And here: VMware KB: Estimating the time required to consolidate snapshots for VMware ESX and VMware ESXi

Contributing factors

The time required to commit snapshots is directly related to:

• The aggregated size of the delta files.
• The virtual disk snapshot chain depth (the number of delta files for a given virtual disk).
• The total overhead size of the snapshot delta disks. This is directly related to the aggregated size of the deltas. If there is a large number of blocks to analyze, it significantly increases the number of reads for analyzing the metadata, thus increasing the overall time for consolidation. For more information, see Creating a snapshot for an ESX/ESXi virtual machine fails with the error: File is larger then maximum file size supported.
• The storage array performance including, but not limited to, storage processor performance, infrastructure contention/bottlenecks, hardware acceleration, the number of physical disks, the number of spindles, disk speed, and RAID configuration.
• The type of data contained in each block (zeros vs. random data).
• The load on the host, which is responsible for resource management and prioritizing tasks.
• The disk I/O activity of a powered on virtual machine having a direct impact on how fast the current delta files are growing. For example, a database or email server virtual machine may be extremely I/O intensive.

Notes:

• The number of blocks that need to be read/written cannot be determined if there is more than one delta file to consolidate. This is because duplicate copies of the same block is possible.
• If there is only one snapshot, all blocks of data in the delta file are written to the base disk. When there are multiple delta files, all blocks in all snapshots may be unique and may have to be written to the base disk in a worst case scenario. The number of reads in this scenario is equal to the number of writes in addition to metadata read operations.
• If disk consolidation is started when the virtual machine is powered on, an additional delta file is created to track the modified blocks, which is finally written to the base disk at the end of the consolidation. However, no additional delta file is required when deleting only one snapshot which is not the current one.
• Virtual disk snapshot consolidation is a very I/O intensive task and may require extended periods of heavy reads and writes. Consolidating snapshots during production hours may impact other virtual machines running on the same datastore.
• Hosts running ESXi/ESX 4.0 Update 2 and later use an optimized method to commit snapshots. For more information, see the VMware ESX 4.0 Update 2 Release Notes.