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Enterprise Backup Solutions - Disk-to-Disk vs. Tape Drives

pdlarue asked

I'm trying to climb out of the box here.  Why would one use tape drives instead of disk-to-disk or RAID system for backups?  Any thoughts on reliabilty on which way is better?  Any opinions?  Any information is all good.

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Tape backup solutions are more cost effective than hard drives if you are archiving and keeping huge amounts of data. For example, if you had a large data set and you wanted to keep many versions, stretching back in time. Eventually, the low cost per GB of the tapes would make up for the high cost of the tape drives.

Be careful though; I have never dealt with tapes, but I have often read in forum postings that some types are rather less reliable than one might hope. It would be especially important, then, to test a backup set from time to time to make sure everything will work.
Almost every client I have worked with that backs up to disk, either just as a plain disk or disk as a virtual tape library they all move the data to tape. Tape goes off site, encripted, WORM, etc.

Except for small shops tape and not disk is the final destination of data for long term storage.

As for disaster recovery off site storage is a must. Now that can be accomplished with disk in a number of ways and even for small shops such as the online backup companies. So tape is not a must for that. However there are a number of companies that by law have to keep long term records and often a media that can not be changed is needed. That used to mean optical but for a long time now WORM tape has taken over that place.

All this is fine for them but the bottom line is what works for you and your needs. That depends on the type of data and application. For example medical records must be secure. Graphic houses keep all image data for ever and frequintly need to restore data based of date. You provided no information on your setup or data, so all that can be done is tell about others, which may or may not be applicable you your case.
>>As for disaster recovery off site storage is a must...

Absolutely. Pdlarue, you ask why one might not just use a RAID array as a backup solution. Bear in mind that a fault-tolerant RAID array only protects against one cause of data loss: a mechanical (or electrical) failure of an individual drive. There would be no protection from: a lightning strike frying everything plugged in at that moment; someone stealing the entire computer; the computer's power supply going bad and damaging the whole computer; floods or fires; user error; a software bug; a virus, especially if it's a Windows machine; etc.

For these kinds of reasons, whatever type of backup media you use, one of the key principles of backing up your stuff is to ALWAYS have offsite storage. In a different geographic area, if that's at all possible. If you were backing up onto external hard drives, then, you would need at least two (even if all your data would fit onto one), so that all your data and backups would never, ever, be in the same building, plugged into the electrical grid, at the same time.

For Enterprise class solution you should be going with the Disk-to-Disk-to-Tape solution.

Backup to disk to return the 'backed up' system into the 'front line' as soon as possible.

Then backup the 'disk backup' to tape for offline storage - at your leasure (including re-tries for the dodgy tapes).

The obvious attraction is that you can restore from disk, reducing the recovery time - but have tapes in case the roof piles in ( Disaster Recovery ).

Most Valuable Expert 2015
leew has a good backup howto on his site, here is his link:

The modern world is moving to disk-to-disk-to-tape back-ups.  disk-disk gives you plenty of flexibility and potential speed, but tapes are for the longer term storage.

There are some very simple advantages for tape:
Cheap - in the long haul, tape is far cheaper than disk to purchase
Portable - Tapes are easy to move off-site etc.  Yes, you can do the same with disks but generally disks weigh a lot more than tape - that means it has more momentum when it hits the ground!
Proven - tapes have been used for long term storage for aeons.  Various studies have shown DLT's, LTO's and the rest as being viable for 10-30 years, depending who you listen to and how they're stored.  In contrast, how long does a disk last?  Some manufacturers give 5 year warranties, but this is on the assumption that the drive is used.  How long does a drive last if its stored off-site with no power etc.  I've seen no testing for that scenario so how can you trust it?  and if you listen to Steve Gibson (http://www.grc.com/sr/spinrite.htm) then hard drives are SURE to fail if left unattended for long periods.

The other thought is interfaces:  disk has moved through various flavours of SCSI and now to SAS, we've had IDE then SATA and SATA2.  looking at my arrays at work, none of my old 4.3GB disks would plug into a modern server.  But I can still restore a system from '98 using DLT or DDS, 'cos the newer drives still read the old stuff.

Finally(?) there's design.
disk is designed to be active; for on-line access - ie, being powered up.
tape is passive - ie, it doesn't need to be powered up to work (the tape drive is the powered bit).
So if you're gonna store data for 10 years on either medium, you should do so as its designed:  ie, keep the disk powered up for 10 years, replacing failed drives as required, or store the tape on a shelf somewhere.  Think about electricity and cooling costs for the disk arrangement in this comparison!



This was all great information!  I wish I could give you all 500 points.  Thank you so much for your input.

Have a great weekend,