Avamar: Client backup performance tuning for datasets with low ratio of files to folders

The Avamar client "avtar" process is optimized to work well with most datasets while avoiding excessive resource consumption.

Occasionally "avtar" may encounter datasets whose characteristics are different to, and may not play to the strengths of, the default tuning parameters chosen by engineering.

Datasets for most file system backups typically have a file to folder ratio of around 10:1.

Datasets where there is a low ratio of files to folders, such as 1:1 or 2:1, may experience reduced performance, all other things being equal.

The file to folder ratio can be checked by reviewing a complete backup log for the following entry.
 

2015-11-18 00:34:32 avtar Info <5156>: Backup #75 timestamp 2015-11-18 00:24:43, 4,007,032 files, 1,974,043 folders, 1,589 GB (2,680 files, 419.4 MB, 0.03% new) 

For datasets with a low file to folder ratio, it can be helpful to tune the "--maxopendirs" avtar parameter from the default value of 100.

The "maxopendirs"parameter controls how many directories avtar can have open at one time and helps allows avtar to work more efficiently. With appropriate tuning, files-per-hour backup performance may increase. The trade-off is typically a slight increase in memory utilization by the Avamar client. 

The following log extracts are from the same client, same dataset with no other alterations made other than to "maxopendirs".

We can see how, as "maxopendirs" increases from 100 to 1000, avtar consumes more memory and achieves a higher files/hour backup performance.
 

maxopendirs=<default>

• • Peak avtar memory utilization = 492 MB

2015-11-08 09:30:19 avtar Info <5156>: Backup #38 timestamp 2015-11-08 09:21:48, 3,995,129 files, 1,965,847 folders, 1,671 GB (172 files, 32.25 MB, 0.00% new)
2015-11-08 09:30:20 avtar Info <6083>: Backed-up 1,671 GB in 659.14 minutes: 152 GB/hour (363,668 files/hour)

maxopendirs=200

• • Peak avtar memory utilization = 526 MB

2015-11-12 09:32:47 avtar Info <5156>: Backup #54 timestamp 2015-11-12 09:23:31, 3,998,280 files, 1,969,137 folders, 1,546 GB (4,121 files, 688.2 MB, 0.04% new)
2015-11-12 09:32:47 avtar Info <6083>: Backed-up 1,546 GB in 667.61 minutes: 139 GB/hour (359,336 files/hour)

maxopendirs=800

• • Peak avtar memory utilization = 605 MB

2015-11-14 07:45:58 avtar Info <5156>: Backup #62 timestamp 2015-11-14 07:36:24, 4,003,390 files, 1,971,781 folders, 1,561 GB (3,816 files, 645.8 MB, 0.04% new)
2015-11-14 07:45:58 avtar Info <6083>: Backed-up 1,561 GB in 559.08 minutes: 168 GB/hour (429,638 files/hour)

maxopendirs=1000

• • Peak avtar memory utilization = 597 MB (fewer sample points available due to the faster backup)

2015-11-18 00:34:32 avtar Info <5156>: Backup #75 timestamp 2015-11-18 00:24:43, 4,007,032 files, 1,974,043 folders, 1,589 GB (2,680 files, 419.4 MB, 0.03% new)
2015-11-18 00:34:32 avtar Info <6083>: Backed-up 1,589 GB in 144.70 minutes: 659 GB/hour (1,661,482 files/hour)