Virtual servers put pressure on backup


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Some help from point products

There are a few "point products" designed specifically to address VM backup that can be incorporated into the backup process to address some of these issues. VizionCore Inc. was early to the market with its vRanger Pro product, and has been doing VMware backups longer than anyone else. Another popular alternative is esXpress from PHD Virtual Technologies. Both products are able to do VMDK-level full and incremental backups, and file-level restores with or without VCB. The two products think and behave very differently, however, so make sure you find the best match for your environment. Note that volume-level backups with both products still require reading the entire VMDK file, even if they only write a portion of it in an incremental backup.

Source deduplication

You can also use source deduplication backup software, such as Asigra Inc.'s Asigra, EMC Corp.'s Avamar or Symantec's NetBackup PureDisk. The first way source deduplication backup software can be used is by installing it on the VM where it can perform regular backups. However, source deduplication backup requires fewer CPU cycles and is less I/O-intensive than a regular backup (even an incremental one), so it significantly reduces the impact on the ESX server. Doing backups this way also lets you use any database/application agents that the products may offer. The downside is that you're not usually able to do a "bare metal" restore of a VM if this

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is the only backup you do.

Some products take this approach a bit further by running a backup inside the ESX server itself, capturing the extra blocks necessary to restore the virtual machine. But this method requires the backup app to read all the blocks in all of the VMDK files to figure out which ones have changed. That could significantly impact I/O on the CPU as it calculates and looks up all those hashes.

CDP and near-CDP approaches

Continuous data protection (CDP) and near-CDP backup products are used in much the same way that deduplication software is used. They're installed on your VM and back up virtual machines as they would any other physical server. The CPU and I/O impact of such a backup is very low. Most CDP software won't allow you to recover the entire machine, so you'll need to have an alternative if your VM is damaged or deleted.

Near-CDP-capable storage

So far, all of the methods covered have as many disadvantages as advantages -- if not more. But there's a completely different solution that merits serious consideration: Use a storage system that has VMware-aware near-CDP backup already built into it. (Keep in mind that near-CDP is just a fancy name for snapshots and replication.) Dell EqualLogic, FalconStor Software Inc. and NetApp all have this ability. Other storage vendors are developing similar capabilities, so check with your storage vendor.

The concept is relatively simple. VMDKs are stored on their storage, and each has a tool designed for VMware that you can run to tell it to back up VMware. VMware then performs a snapshot similar to what it does for VCB, allowing your storage box to then perform its own snapshot of the VMware snapshot. Replicate that backup to another box and you have yourself a backup.

This was first published in August 2009

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