Last updated on Monday 28th of February 2022 08:52:48 PM

©VMWare Backup - What type of storage to use: local disks, NFS or iSCSI

 Please note that this post is relative to old deprecated software ©XSIBackup-Classic. Some facts herein contained may still be applicable to more recent versions though.

For new instalations please use new ©XSIBackup which is far more advanced than ©XSIBackup-Classic.

If you are an ©ESXi user, you've probably come across this two questions a number of times:

• What is the best type of datastore I can use?.
• Are there any especial considerations to take on account when using a datastore to backup VMs to?

©ESXi offers basically three ways to set up datastores: local disks, NFS and iSCSI. There is a much wider range of real possibilities, as this three categories comprise many different hardware options and technologies. As the different number of possible combinations is almost endless, we'll fix some variables and limit our scenario to local SATA disks, gigabit Intel NICS and NAS devices, such as QNap or Synology (decent switches are a must to be able to reach speeds close to the NIC's theoretical limit). From this limited set of resources, you'll be able to extrapolate more complex scenarios, up to some point.

By choosing NFS or iSCSI, you are limiting your speed to the NIC's limits. You now may think loud: "I can use multipathing". Yes, of course, but multipathing will not offer you the same real speed as a local disk array and depending on the type of multipathing/ port trunking you use, each file will most of the times be sent through one NIC. Parallelizing data transfers across multiple NICs is great when you have a lot of smaller files, but might be useless when transferring huge monolithic files. Of course, the real advantage of multipathing is being able to run multiple VMs, taking advantage of an extended throughput. But copying files out of your datastore or ©ESXi host is something different.

Local disks

Let's start by analyzing use of local storage media. We have constrained ourselves to simple SATA, but you may improve the speed to your local disks by using some more powerful technologies, like: Arrays, SSD, SAS, FC, etc... This will be the fastest price to speed ratio option among all commented above. Thus, using local disks is the recommended way to mount a datastore. NAS devices will be a great asset if we can renounce to speed in sake of placing our data somewhere outside the server. Using a NAS server which is physically placed by the ©ESXi server is useless, if this is your case, just use an eSATA enclosure directly connected to your SATA controller, and you will improve your backup speed and save money at the same time.


NFS is the fastest data transfer protocol available in ©ESXi. NFS 4.1 allows multipathing, but not all NAS devices support it at the time of writing this, and, as explained above, will not improve backup speed in a one to one copy scenario. Multipathing is great, and a must when you have multiple VMs running in a NAS device, but as stated before we are focusing on a different task: backing up the VMs, so forget about multipathing, it won't offer you aggregated speed for backups.

The downside of NFS is that you cannot format it as VMFS, NFS links will use the filesystem present at the NAS device disks. This has some advantages too, as common filesystems, such as ext3, ext4, vFAT, BTRFS, etc... have a huge number of available inodes, which is in turn a great asset to XSITools and deduplication, but it's not that good when you perform © OneDiff backups, as the Trivial Check that it performs upon VM backup will loose the ability to do one of the matching tests on the .vmdk disks: used size matching. You can always perform a full hash check on the disks by means of the --certify-backup argument, but that will take longer. If you can perform OneDiff backups to VMFS volumes, you will achieve a great degree of certainty with a quick check (Trivial Check).


iSCSI is a protocol that allows you to mount remote disks as if they were local to your server, so it sees them as block devices. This is awesome, but as everything in life, just as long as you know how to take advantage of it. iSCSI works through the network, so it will add an additional latency in comparison to using a local SATA disk. You can take advantage of mutipathing, it will be of little help for backups though, but it has an advantage: it will allow you to format the mounted volume as a VMFS device.

So, you should choose your datastore type taking on account the pros and cons of each technology to best suit your needs. If you want a datastore to perform backups, local disks will be the best option for full backups and OneDiff backups, NFS will be the fastest protocol to use with XSITools, whereas iSCSI can be a way to be able to use VMFS formatted volumes and at the same time keep the storage devices separated from the ©ESXi host/s through a 1 gigabit or 10 gigabit network.

Full backup OneDiff XSITools
Local HD  

Daniel J. García Fidalgo