Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

I want to know about snapshotting.

Amazon says that they make

  1. Incremental backups
  2. Only charge for the data chnaged between snapshots

Now my question is let us suppose the only data which change is only coding files which will only be few MBs every week even not that

So does not matter if i have 1000 backups or 10 backups. because the differnce wont be there in any subsequent snapshots and i wont be charged.

Am i right.

I mean if i have 10GB snapshot of First data and suppose that stores full 10GB

now let us suppose i take snapshots every hour and provided data does not chnage for one month.

so i will be having 24*30 = 720 snapshots. Without any additional cost because data is not changing.

Ami right or i am missing something

share|improve this question
    
I don't know much about Amazon's services BUT: If snapshot is a snapshot in the VMWare sense, having many or long term snapshots is not a good idea. If this is closer to a rsync with hardlinks solution.... It is conceivable that you could have many thousands of 'snapshots' with nominal over head in storage, but if you intend to give amazon money (and you should if you expect to keep 720 snapshots), I would take your concerns DIRECTLY to their support team. They will be best equipped to handle your situation. –  lVlint67 Jul 13 '13 at 4:08
add comment

1 Answer

up vote 0 down vote accepted

Copy-on-write snapshots do not consume space unless their data has changed, which is why they are not going to charge you for the space.

There will be meta-data that needs to be stored for the snapshot. This will be nominal, but I can't guarantee that it will be free. Also, it's virtually impossible to change nothing between two snapshots. Whether it's a log file being written to, or a ticker ticking over, etc. Something will be changing.

However you really don't want 720 snapshots. What are you actually trying to achieve? EBS volumes seem to have a limit of 500 snapshots anyway, which also seems like a bad idea.

share|improve this answer
    
I just thinking of having cron jobs running twice and having two snapshots per day. My data is not going to chnage. Actually i try installing something new every day so before doing anything , i make snapshots. i was not sure whether that is going to charge me or not. But thats fine. –  MOtaro Site Jul 12 '13 at 4:03
    
Making a snapshot prior to installation is a wise move; but once the installation is stable, you will want to remove that snapshot. I once had to remove a 75-day-old snapshot from a database server. It was killing performance for one, and it took 14 hours to merge the snapshots back into the main image so the snapshot could be removed. Usually you only want snapshots for short-term. If you want long-term, look at other backup methods. –  Mark Henderson Jul 12 '13 at 4:06
    
I dont get you . 1) How can old snapshot kill performance . 2) what do u mean by took 14 hours to merge. what is that –  MOtaro Site Jul 12 '13 at 4:08
    
1) There is a performance hit the first time you change data since a snapshot. It's not much, but do it often enough and it adds up. The older the snapshot, the more data will have changed between now and then, which leads to 2) when you remove a snapshot, the number of snapshots and the time between them impacts how long it takes to remove. While it's removing you basically thrashes the IOPS of the storage to its maximum merging all your changes back into the underlying disk. The fewer changes, and the fewer snapshots, the less there is to change. –  Mark Henderson Jul 12 '13 at 4:34
    
A similarly related issue is one of backups - many backup strategies often make a snapshot, then move the snapshot off-site, and delete the snapshot. It can take several minutes to simply remove a 5-minute-old snapshot if you have a very old snapshot sitting in there (speaking from experience) –  Mark Henderson Jul 12 '13 at 4:35
show 1 more comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.