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When assessing tape backups vs online disc backups, which of them ensure better protection from integrity incidents.

For example, if the system is compromised by attacker or virus or malware and I know the date when it happened, i can roll back data backup from tape before that incident and it will be fine. In online and disc backup solution I can not be so sure, because the backups also can be harmed as they are available from the same systems where the malware,virus etc lives.

So what do you think about tape vs disc? Particulary in financial institutions.

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There are good comparison available on the internet you can read "eversyncsolutions.com/disk-vs-tape.html"; –  Ali Ahmad Feb 13 '13 at 7:24
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This question is not about "choosing between tape and disk", it's about "should backups be accessible/modifiable from production?". As a sysadmin, I'd like to say that if your backups can be modified by a production system while they are in storage, they are not backups. You might call them that, but they are not. –  Ladadadada Feb 13 '13 at 8:41
    
Ladadadada, how do you ensure that online, disc backups are not modified? For example, VMWare machine backups or SQL dumps? –  jam Feb 13 '13 at 8:44
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In my case, the backup system connects to the client systems to perform the backups. The client systems have no way to connect to the backup system. I also store alternating backups on separate filesystems. You could remount the filesystem as read-only after each backup too. These measures were designed to prevent accidental deletion and not protect against malicious modification however they do certainly make the latter somewhat more difficult. Storing hashes of the backup files offline would detect violations of integrity. –  Ladadadada Feb 13 '13 at 9:28
    
@jam If you have a SAN, you're likely to be able to physically separate your backup server from your production network - it gets access to the storage fabric, but nothing else. Essentially this works as if you're backing up, bit for bit, a disk that your operating system doesn't recognise - it is highly unlikely you can mount a successful exploit that way. –  Bob Watson Feb 13 '13 at 9:37

3 Answers 3

It truly depends heavily on your specific and current capabilities. You need to ask yourself the following questions:

  1. What are our current capabilities? That is, what infrastructure currently exists, do you have an enterprise SAN, do you have a tape library, a tape robot, what does your current backup solution support?
  2. What are your retention requirements? Are you subject to any regulations or legislation that require you keep backups for a length of time?

Some things to keep in mind about the two formats.

  1. Disk is faster and cheaper.
  2. Tape has a longer proven track record for storage.
  3. Disk often requires fewer components, in that it is black-boxed into the SAN.
  4. Tape will require, at minimum, physical tapes, robot, and storage facility.
  5. Tape expertise is aging out. Kids these days aren't as familiar with it.

The question of which ensures higher integrity is really hard to answer since it depends entirely on what time frame you're interested in. Maintaining integrity over 7 years is a very different ball of wax than 30 days.

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Bob put together a very good summary, however I think it's important to note that newer tape (LTO5 and LTO6 and beyond) are working to close the gap in speed due to LTFS (Linear Tape File System). Some good reads: https://www.fujifilmusa.com/products/tape_data_storage/case_studies/pdf/WhitePaper_LTFS-TakesTapeToNextLevel.pdf and http://www.spectralogic.com/index.cfm?fuseaction=members.docContactInfoForm&DocID=3427

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These days it doesn't actually make a huge difference. Or rather, it depends very strongly on your backup plan, disaster recovery plan, your RPO and RTO and the scenarios you expect to want to recover from.

In any modern environment; you're likely to also have some sort of SAN. Your backup solution should interact with the SAN, but not the rest of the network; this allows you to back up data without exposing your backup solution to risks associated with the hosts you're backing up (this is a generalisation).

The decision between disk and tape should come down to your environment and your requirements. If you need to store your data for a long time: tape, properly handled can last decades, so as long as you test their integrity every ~10 years, you should be pretty safe. It is cheaper per GB (in the order of something like 90%), and the principles behind storage and retrieval are well understood. It is however, very, very slow compared to disks.

Disk can potentially be always available, it is a lot faster and lends itself to replication via WAN/etc. - but you generally have to leave them on and running to verify their integrity, and buying more disks can be a limiting factor if you're keeping your data for a good amount of time (how many fit in your array?).

In most environments, you have a combination of disk and tape; certainly for environments with any sort of compliance overhead. Disk backups deal with replication and hot site DR, tape deals with historic backups and long term storage.

To answer the question:

Is physical tape backup better than disk to ensure integrity?

It depends on how long you're storing, your backup cycle, and what you're backing up for (will you need the data in a hurry?).

So what do you think about tape vs disc? Particulary in financial institutions.

I think any serious environment will likely have both. Particularly financial institutions that require high availability and minimum downtime - if their server room floods, you'd expect them to be up at Site B very quickly (so, from disk), and if they need to dig up accounts from 30 years ago, I'd expect them to be able to by going to their tape library.

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Thanks BOB for your explanation! Very useful. –  jam Feb 13 '13 at 8:10

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