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Avamar - Full Backup Understanding
I have read that Avamar only does a "Full" backup. Is this true?
If Avamar only does full backups why would the same server some days take 15mins to backup and others days it may take 1 hour to backup?
ionthegeek
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October 12th, 2016 15:00
Avamar backups are "incremental forever" but are restorable as though they were run as fulls.
tl;dr: Change rate
I'm assuming you're talking specifically about filesystem backups. Database backups work a bit differently but I can talk about that if you have questions there. I've simplified a bit for clarity.
For filesystem backups, Avamar will "stat" each file and generate a hash of the file attributes. It then looks this hash up in the file cache and if it finds the hash, it will just mark the file as part of the new backup and move on. If the hash is not found in the cache, the file will be re-chunked. The client just marks unmodified chunks as part of the new backup so they don't have to be re-sent. Any modified chunks will be sent to the storage.
Any time difference is normally a result of a higher (or lower) file change rate. 90% or more of the client's performance gain is related to the cache. Since modified files need to be read from the disk in full to determine if any chunks inside the file have changed, having many modified files or large modified files will result in a longer backup time.
One other possibility is that some days there is contention for I/O resources and some days there is not. Backup performance for any individual client is generally limited by the available I/O capacity of the client system.
Avamar Exorcist
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October 13th, 2016 01:00
If you have a reliable source of coffee and would like to do some background reading on what Ian discussed, take a look at the following articles
Dez47
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February 2nd, 2024 11:51
@ionthegeek Hi Jon
I have a similar question about how Avamar does SQL database backups and your reply about filesystem backups is the only explanation I've ben able to find about the why Avamar is set to take a full backup everyday but the time taken for it can be very different.
You said that database backups work differently to filesystem backups so would you also be able to explain how come after a database is restored the time taken to take the first full backup is much longer than any full backup taken afterwards please?
(edited)