Avamar: NDMP Backup Runs Level Zero Despite Existing Incremental, Extending Job Duration
Summary: Network Data Management Protocol (NDMP) backups default to level 0 if no level 1 backup is found within the last 30 labels. This article lists the steps to increase the search limit.
Symptoms
Unexpected NDMP backup behavior:
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NDMP level‑zero (full) backups take an unusually long time to complete.
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Avamar initiates a new level‑zero backup even though a successful incremental backup already exists for the same file system.
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The backup logs indicate that no usable previous backup was found, prompting a full backup.
Relevant log excerpts:
2014-05-19 20:49:55 avndmp Info <9573>: [snapup-/root_vdm_37/xxx] No previous suitable backup found, will perform level zero backup.
2014-05-19 20:49:55 avndmp Info <9590>: [snapup-/root_vdm_37/xxx] Backup on volume '/root_vdm_37/STFS4/': mode 'Full', level '0', base dump date '0'
Additional log details showing the incremental search process:
2014-05-19 20:49:54 avndmp Info <9538>: [snapup-/root_vdm_37/xxx] Selecting backup out of most recent 30 to use as incremental base for volume:'/root_vdm_37/xxx/'
2014-05-19 20:49:54 avndmp Info <9552>: [snapup-/root_vdm_37/xxx] Spawning '/usr/local/avamar/bin/avtar' (avtar --backuptag="/root_vdm_37/xxx/" --format="xml" --count="30" --backups --vardir="/usr/local/avamar/var/xxx-ndmp-hostname2.x.com" --bindir="/usr/local/avamar/bin" --sysdir="/usr/local/avamar/etc" --acnt="/NDMP/xxx-ndmp-hostname2.x.com" --id="backuponly" --ap="backuponly1" --server="avamar.x.com")Cause
The Avamar avndmp plug‑in determines whether an incremental NDMP backup can be performed by querying the avtar utility for a suitable previous backup.
The utility only examines the most recent 30 backup labels.
When the last successful backup for the file system is older than those 30 labels, avtar reports that no suitable backup exists, causing avndmp to start a new level‑zero (full) backup.
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The incremental‑search window is fixed at 30 backups by default.
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If the previous successful backup falls outside this window, the system incorrectly assumes that a full backup is required.
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This behavior results in unnecessary long full NDMP backup runs even though a valid incremental base is available.
Resolution
How to Increase the Incremental Search Limit for NDMP Backups:
1. Log in to the Avamar accelerator node with an account that has root privileges.
2. Go to the client‑specific directory that stores NDMP configuration files:
For example:
cd /usr/local/avamar/var/[CLIENT_NAME]
3. If an avndmp.cmd file does not exist, create it. If it exists, edit the file.
4. Add (or modify) the flag that controls the incremental search limit. Replace n with the wanted number of previous backups to search (default is 30):
--limit-incremental-search=n
Example to search the last 100 backups:
--limit-incremental-search=100
5. Save the file and ensure that its owner is avamar and has appropriate permissions (typically 600).
6. Restart the Avamar services so the new setting takes effect:
systemctl restart avamar
init system, use the appropriate command (such as, service avamar restart)
Verification:
1. Initiate an NDMP backup for the affected client.
2. Monitor the Avamar logs (for example, /usr/local/avamar/var/log/avndmp.log) for entries similar to:
[... ] Selecting backup out of most recent n to use as incremental base for volume:'/.../'
(The value of n should match the number configured.)
3. Confirm that the backup runs as an incremental (level > 0) when a usable previous backup exists. Check that the backup duration is reduced compared to a full (level 0) run.