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Proposed backup strategy question


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Greetings all,


I'm tasked with revamping our Retrospect 7.5 backup system based on a desire by our IT director to have "daily" backups copied to tapes. I of course convinced her to allow for a D2D2T strategy, because I have a feeling the disk will allow for a quicker recovery should the need arise. We have about 300GB of data that will be backed up daily and I purchased a 2TB ReadyNAS (1.3GB usable since it has a hotswap drive) for the disk storage portion.


I plan to have 3 partitions of about 430GB and to run three scripts...Week A, Week B, Week C...copying to their respective areas on the NAS, and into seperate backup sets...Set A, Set B, Set C.


My thought it that this would give us 15 days of recoverable snapshots onsite, and keep the catalog files manageable...and with each running in a 5 day week, it shouldn't fill up the 430 GB area before a recycle is done every 3rd week (or would it?).


Then for offsite storage, we have LTO2 Tapes, and I'd like to transfer to tape daily (based on orders from on high) either snapshots or backup sets...not sure which yet. My quandry is what the most efficient way to accomplish this and if copying snapshots is the chosen route, what effect does the recycle backup have (if any) on the snapshots that are on tape prior to the date of a recycle backup? Would running the recycle invalidate a catalog thus rendering the data on the tapes useless?


Our goal is to eventually have 3 months of recoverable data on tape. Yes I realize the amount of tape involved, but that's not my call. Ultra conservative IT director that has been burned in the past by a backup system that didn't perform when it mattered.


And for the last part of the equation, is there a way to then Re-use the tapes after the 3 month period. (Yes I'd be making a quarterly backup for permanent storage).


Thanks for any information you guys could provide...I think I'm on the right track, but if not, will someone update my GPS :tongue2:


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An excellent question, StateITtech.


Lets give you some answers and advice.


Q. 300GB of data into a 430GB disk based backup set, will it fill the set before 5 backups are taken?


A. It depends on the data. If you're talking an exchange server information store, or a SQL database, then you're basically talking "one file", and a such you can probably back it up about twice, assuming it compresses a little. However, seeing as you're posting in the professional group, I will assume you're talking about a healthy mix of files involving mainly a couple of entire PCs and all the stuff people keep on them. If this is the case then the Retrospect recommendation is to size the backup set at twice the size of the data you will keep in it, so that PLENTY (months worth) of snapshots can be fit into it.


In practice, if you are mainly talking office documents, and enable compression, then 300GB will easily fit into a 430GB backup set with multiple snapshots possible, possibly up to 20 or more.




Q. Should I transfer snapshots or backup sets to tape?


A. Please read the D2D2T whitepaper. However to answer your question, since you will be backing up to disk every night, the basically creates a snapshot each night. During the day it makes sense to transfer only this snapshot to the tape. So transfer snapshot is the way to go.




Q. What effect does the recycle backup have (if any) on the snapshots that are on tape prior to the date of a recycle backup?


A. Simplistically answered, a Recycle backup wipes the target media being backed up to before the backup begins. So performing a recycle backup to a tape will wipe the tape and then backup to it. Wiping a tape or disk via a recycle backup also wipes the catalog along with it. Note that each backup set has its own distinct catalog, which is simply a database of all the files in the backup set.




Q. Would running the recycle invalidate a catalog thus rendering the data on the tapes useless?


A. Again, a recycle backup wipes the media, and also empties the catalog pertaining to that media, so there will never be an invalid catalog.




Q. Is there a way to then Re-use the tapes after the 3 month period.


A. Yes, perform a recycle backup to them, which will wipe the tape and write the current data.




Q. Will someone update my GPS?


A. ok, here goes. Consider this alternate configuration and benefits:


Each of the disk based backup sets should have grooming enabled and will only rarely be recycled. This way each of these sets will accumulate snapshots that reach way back in time, much further than the 15 days you had planned for. If you switch from 3 to 2 sets, then each set will be 640GB, which exceeds the recommended minimum sizing, enabling deep history (eg 3-8 months worth) to be maintained on site.


On a daily basis you transfer the snapshot from the night before to tape. Depending on factors, you may find that you can fit 20 snapshots onto 1 tape. Once the tape fills, you can either add tapes and keep transferring snapsnots, or you can recycle the tape and then transfer the snapshot. Obviously if it recycles, then anything stored on that tape will be lost, which comes back to how many tapes you have and how long you need to keep snapshots for. You said three months, and you appear to require duplicates, so have three tape sets, and keep adding tapes to each one as needed until 3 months are up and they can start being recycled.



Some definitions:



Snapshot: A list of all the files on the computer at a point in time that also exist in the backup set.



Backup Set: A collection of snapshots and all the files listed in the snapshot.



Grooming: The removal of older snapshots and files unique to those snapshots to make room for new snapshots and their files. The number of snapshots removed is based on how much space is needed to keep the new snapshot that will be added.

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Thanks so much for the detailed response. Some of the items you've mentioned were on my radar as well...especially going from 3 disk backup sets down to 2. I'm testing how much data will fit on the disk right now during the day, so I don't interupt our current nightly backups to tape, but it is starting to look like 2 sets may be the way to go, since the entire reason for going to NAS was to have easier access to file recovery onsite should the need arise.


The files we will be backing up are indeed a mix...An Exchange server, a file server, 4-5 application servers, some critical PC's, etc.


I currently run four scripts at 2 weeks apiece putting everything to tape, and then run a recycle at the end of the 2 weeks, for each set. This however only gives us 8 weeks of recovery, and due to a poilcy change it needed to be extended.


I took this opportunity to put a NAS in place, and I'm just having some "growing pains" figuring out the most efficient scheme to get data from the disk to tape, while being able to reuse the tapes after their 3 month rest in the archives offsite is up.


Thanks again for all the info.



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