Reminder: Copies of data on the same Primary Storage is not a backup solution.

I find it difficult to understand how any Account Manager, Sales Engineer or Consultant can go to a customer, who is at least in part trusting their statements & opinions when considering new product/s and make claims that a product is performing a “backup” function when the data remains on the same primary storage system (failure domain).

Most vendors have metadata or snapshot based options which allow space efficient recovery points to be maintained on primary storage for fast recovery and any vendor worth talking to will also tell you that until a FULL COPY of the data is maintained off the primary storage, it is NOT a backup.

Some vendors will play games and try and differentiate and say they don’t use snapshots and they are somehow amazing and unique. In reality, they can say whatever they like, but if the end result is the data is only maintained on primary storage, then its not a backup and you should not treat it like one.

In the old days, it was fairly common to have Primary data on one set of LUNs/RAID packs and for customers to keep full copies of data on different LUNs and underlying RAID packs before offloading to tape.

While the copy of data remained on primary storage, it at least meant that in the event the RAID pack/s hosting the primary data failed (e.g.: Double disk failure in a RAID 5) then data could be recovered and if not, then the customer could restore form tape.

As storage became more intelligent, keeping the full copy became less popular in favour of snapshot or metadata based copies. This makes a lot of sense as it reduced the overheads significantly while achieving a business outcome which allows for fast recovery in the event the Primary Storage is not impacted.

However, the requirement for data to be kept off the primary storage remains, as no matter what vendor you choose, its possible to have a catastrophic failure which means the snapshot/metadata copies on primary storage may not be available.

Also promoting that snapshots (or any form of metadata copies pointing to the same underlying blocks) are this amazing new data reduction technology which achieves 60:1 or 100:1 data reduction is misleading at best in my opinion.

So let’s cover off a few things:

Question 1: Are snapshots or metadata copies of data stored on primary storage a backup?

Answer: No

A snapshot or metadata based copies simply makes some data at various levels such as a vDisk, Virtual Machine , LUN , Container etc read only and new writes (commonly referred to as delta changes) are written elsewhere.

The data still resides on the same storage, meaning if data loss occurs (say multiple drive failures or storage system software issue) its possible if not probable that the data being referenced by the snapshot/metadata and delta changes will all be lost (or at least unavailable) in some failure scenarios depending on the vendor.

So having snapshot or metadata based copies on primary storage as a backup without at least one full copy in a seperate failure domain is simply asking for trouble.

Snapshots/metadata copies are only the first step in a backup solution which must ensure data is stored in at least two locations (different failure domains) so that data can be recovered in the event the primary storage is lost/unavailable for any reason.

Question 2: Are snapshots data reduction?

Answer: No

Snapshots and metadata copies don’t reduce data, they simply avoid creating and requiring the storage to store more data than is necessary to keep the point in time (or Recovery Point) copies (not backups) of data.

This is Data avoidance, not data reduction which cover this topic in more depth in a previous post: Deduplication ratios – What should be included in the reported ratio?

Now don’t get me wrong, Data avoidance (e.g.: Snapshots, Intelligent Cloning etc) has real value and its something I would recommend customers leverage wherever possible as it generally reduces the overheads on infrastructure significantly which can help achieve business outcomes like more frequent RPOs or faster deployment/maintenance times for VDI.

However making a claim that a customer has 60:1 or 100:1 data efficiency because they are taking frequent snapshots/metadata copies (which in many cases are unnecessary to meet business objectives) in my opinion is misleading customers and worse still, claiming its unique (as in other vendors cant achieve the same business outcome) is just a flat out lie.

Now I work for Nutanix, so let’s use another Vendor as an example, and one which I have lots of experience with from my years at IBM. Take Netapp (a.k.a IBM N-Series), for many years they have supported taking snapshots which are application consistent (via SnapManager) and keeping them on Primary storage. They as with many other vendors (new and legacy) do it in a way which avoids storing multiple copies of data and they redirect on write all delta changes which can be snapped at the next scheduled interval.

This results in the ability to keep lots of point in time copies without storing data multiple times. You could argue this is a ratio of “Insert crazy number here” :1 but the reality is, if the storage you have wasn’t storing 1:1 copies previously (which only a select few legacy products still do), a new solution doing similar isn’t a big step forward even if it could be argued it’s a bit more efficient.

Netapp allows these snapshots on primary storage to then be replicated to secondary storage (SnapVault) which is a different failure domain, with dedicated controller/s and disks. This allows for recovery of all data in the event the primary storage fails or is unavailable. Netapp also allow offload of snapshots to tape.

Many other vendors have similar functionality (and have for a long time) include but are not limited too: Pure Storage, Nutanix, EMC , Dell , IBM, the list goes on.

This functionality is table stakes… Not something unique to any one vendor or something that requires proprietary hardware to achieve.

Any vendor listed above (and others) can achieve the similar levels of data efficiency (if you want to use that term) if they all perform snapshots or metadata based copies at the same frequency. Each vendors implementations vary and each have pros and cons, but from a business outcome perspective (which is the ONLY thing that matters), its table stakes.

Question 3: What are Snapshots/Metadata copies on Primary storage good for?

Answer: They are good for creating recovery points to help achieve Recovery Point Objectives (RPOs) when combined with replication to secondary storage and/or tape/cloud to cater for site loss scenarios. Keeping snapshots on primary storage helps speed up recovery in the event you need to role back to a previous point in time assuming you have not had a storage failure. e.g.: Recovering a file or DB which was accidentally deleted or was corrupted for whatever reason.

So there is value in snapshots/metadata copies on primary storage, but it should not be considered a backup until it is replicated to another location, ideally offsite in a difference failure domain.


Snapshots/Metadata based copies (on primary storage) are just the first step of many in an overall backup strategy. If the data is not replicated to another failure domain, it should not be called or considered a backup.

Marketing Claims of 60:1 or 100:1 data efficiency may sound good, but these sorts of numbers have been and can be achieved by many vendors for a long time. Be very careful when considering new infrastructure not to be mislead by these sorts of marketing claims.

Most vendors don’t market numbers like 60:1 or 100:1 because they understand its table-stakes and misleading for customers, and kudos to those vendors!

Snapshots/Metadata copies regardless of data efficiency ratio are USELESS in the event of a primary storage failure unless a full copy of the data is stored off the primary storage and depending on the business requirements, stored offsite.

I encourage the everyone, especially the industry analysts to help clarify this situation for customers as there is A LOT of mis-information being spread currently which puts customers at risk in the event of primary storage failures.

5 thoughts on “Reminder: Copies of data on the same Primary Storage is not a backup solution.

  1. *Edited to remove vendor name*

    You are right in saying backups should be replicated to a separate failure domain. However, I don’t see how using array-based snapshots as backups is mutually exclusive to this. As an example, lets say you are using CommVault Intellisnap with a storage platform. You have primary storage with Intellisnap snapshots that gets replicated to a secondary storage where data retention is set for longer periods of time. In this scenario you have two failure domains and are using array-based snapshots as backups.

    Without the secondary array, I would agree with you. Thoughts?

    • Hi Nick,

      I believe I covered what you have mentioned, for example in the summary I wrote:

      “Snapshots/Metadata based copies (on primary storage) are just the first step of many in an overall backup strategy. If the data is not replicated to another failure domain, it should not be called or considered a backup.”

      If you don’t feel the article covers the requirement for a full copy of data to be on a second failure domain, let me know and I’ll see if I can make it clearer.

      Thanks for the comment.


  2. Hi Josh

    I certainly agree with your main argument that snapshots are not backup, as they cannot protect against media failure. Other data services within the array or SDS should provide some level of protection against that situation. You cover the first benefit of snapshots, being the ability to provide recovery points for many frequent dev/test requirements. The second is to provide what Gartner calls Copy Data Management, the ability to provide multiple copies of the source data at little to no cost. This is where the dramatic data efficiency numbers come from. The ability to consolidate the 10-15 SAP environments, including Oracle databases, sometimes TBs in size, often needed to provide consistent dev/test/uat/pre-prod/etc. is a huge benefit. These two benefits together can explain many of the extraordinary data efficiency claims we are seeing today.

    Not surprising that Sales or Account Executives confuse these capabilities, Sales Engineers should know better! ☺

    Kind Regards, Peter.

  3. == Disclaimer: Pure Storage employee ==

    I endorse both points Josh is making. At the end of the day, the IT marketing professionals have yet to standardize on an industry term for either.

    Here’s a two suggestions for your readers….

    Storage based snapshots are merely recover points that often provide the means to restore a data set to a previous point in time with the shortest possible RTO. A backup requires recovery points to be stored on a second form of media and ideally stored in a separate data center or location from the source or original copy of the data. Snapshots helps recover from human or system error, where as a backup helps recover from events like hardware failure or data center outage. The former is significantly more common where as the latter should be reasonably considered the cost of doing business (and hopefully will ever be called upon… but never say never)

    If you engage with a vendor who claims greta than 10:1 data reduction – then you need to 1) ask them to explain how the data reduction ratio is obtained and 2) ask them to describe how it differs from alternative / competing solutions. The reality is thin provisioning and snapshots are examples of two technologies that while capacity efficient, greatly skew data reduction results by their inclusion. If one is looking for difference in data reduction capabilities, then one needs to focus on 1) granularity of the deduplication block size, number or compression algorithms, and wether these two data reduction technologies operate globally or across a subset of data.

    Great points Josh. I look forward to the upcoming IPO for Nutanix. Keep up the great work!

    — cheers,

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