Optimize the performance of AzCopy with Azure Storage
AzCopy is a command-line utility that you can use to copy blobs or files to or from a storage account. This article helps you to optimize performance.
If you're looking for content to help you get started with AzCopy, see Get started with AzCopy
You can benchmark performance, and then use commands and environment variables to find an optimal tradeoff between performance and resource consumption.
Run benchmark tests
You can run a performance benchmark test on specific blob containers or file shares to view general performance statistics and to identify performance bottlenecks. You can run the test by uploading or downloading generated test data.
Use the following command to run a performance benchmark test.
azcopy benchmark 'https://<storage-account-name>.blob.core.windows.net/<container-name>'
azcopy benchmark 'https://mystorageaccount.blob.core.windows.net/mycontainer/myBlobDirectory?sv=2018-03-28&ss=bjqt&srs=sco&sp=rjklhjup&se=2019-05-10T04:37:48Z&st=2019-05-09T20:37:48Z&spr=https&sig=/SOVEFfsKDqRry4bk3qz1vAQFwY5DDzp2%2B/3Eykf/JLs%3D'
This example encloses path arguments with single quotes (''). Use single quotes in all command shells except for the Windows Command Shell (cmd.exe). If you're using a Windows Command Shell (cmd.exe), enclose path arguments with double quotes ("") instead of single quotes ('').
This command runs a performance benchmark by uploading test data to a specified destination. The test data is generated in memory, uploaded to the destination, then deleted from the destination after the test is complete. You can specify how many files to generate and what size you'd like them to be by using optional command parameters.
If you prefer to run this test by downloading data, set the
mode parameter to
download. For detailed reference docs, see azcopy benchmark.
Optimize for large numbers of small files
Throughput can decrease when transferring small files, especially when transferring large numbers of them. To maximize performance, reduce the size of each job. For download and upload operations, increase concurrency, decrease log activity, and turn off features that incur high performance costs.
Reduce the size of each job
To achieve optimal performance, ensure that each jobs transfers fewer than 10 million files. Jobs that transfer more than 50 million files can perform poorly because the AzCopy job tracking mechanism incurs a significant amount of overhead. To reduce overhead, consider dividing large jobs into smaller ones.
One way to reduce the size of a job is to limit the number of files affected by a job. You can use command parameters to do that. For example, a job can copy only a subset of directories by using the
include path parameter as part of the azcopy copy command.
include-pattern parameter to copy files that have a specific extension (for example:
exclude-pattern parameter to copy all files that don't have
After you've decided how to divide large jobs into smaller ones, consider running jobs on more than one Virtual Machine (VM).
If you're uploading or downloading files, use the
AZCOPY_CONCURRENCY_VALUE environment variable to increase the number of concurrent requests that can occur on your machine. Set this variable as high as possible without compromising the performance of your machine. To learn more about this variable, see the Increase the number of concurrent requests section of this article.
If you're copying blobs between storage accounts, consider setting the value of the
AZCOPY_CONCURRENCY_VALUE environment variable to a value greater than
1000. You can set this variable high because AzCopy uses server-to-server APIs, so data is copied directly between storage servers and does not use your machine's processing power.
Decrease the number of logs generated
You can improve performance by reducing the number of log entries that AzCopy creates as it completes an operation. By default, AzCopy logs all activity related to an operation. To achieve optimal performance, consider setting the
--log-level parameter of your copy, sync, or remove command to
ERROR. That way, AzCopy logs only errors. By default, the value log level is set to
Turn off length checking
If you're uploading or downloading files, consider setting the
--check-length of your copy and sync commands to
false. This prevents AzCopy from verifying the length of a file after a transfer. By default, AzCopy checks the length to ensure that source and destination files match after a transfer completes. AzCopy performs this check after each file transfer. This check can degrade performance when jobs transfer large numbers of small files.
Turn on concurrent local scanning (Linux)
File scans on some Linux systems don't execute fast enough to saturate all of the parallel network connections. In these cases, you can set the
AZCOPY_CONCURRENT_SCAN to a higher number.
Increase the number of concurrent requests
You can increase throughput by setting the
AZCOPY_CONCURRENCY_VALUE environment variable. This variable specifies the number of concurrent requests that can occur.
If your computer has fewer than 5 CPUs, then the value of this variable is set to
32. Otherwise, the default value is equal to 16 multiplied by the number of CPUs. The maximum default value of this variable is
300, but you can manually set this value higher or lower.
azcopy env to check the current value of this variable. If the value is blank, then you can read which value is being used by looking at the beginning of any AzCopy log file. The selected value, and the reason it was selected, are reported there.
Before you set this variable, we recommend that you run a benchmark test. The benchmark test process will report the recommended concurrency value. Alternatively, if your network conditions and payloads vary, set this variable to the word
AUTO instead of to a particular number. That will cause AzCopy to always run the same automatic tuning process that it uses in benchmark tests.
Limit the throughput data rate
You can use the
cap-mbps flag in your commands to place a ceiling on the throughput data rate. For example, the following command resumes a job and caps throughput to
10 megabits (Mb) per second.
azcopy jobs resume <job-id> --cap-mbps 10
Optimize memory use
AZCOPY_BUFFER_GB environment variable to specify the maximum amount of your system memory you want AzCopy to use for buffering when downloading and uploading files. Express this value in gigabytes (GB).
Job tracking always incurs additional overhead in memory usage. The amount varies based on the number of transfers in a job. Buffers are the largest component of memory usage. You can help control overhead by using
AZCOPY_BUFFER_GB to approximately meet your requirements, but there is no flag available to strictly cap the overall memory usage.
Optimize file synchronization
The sync command identifies all files at the destination, and then compares file names and last modified timestamps before the starting the sync operation. If you have a large number of files, then you can improve performance by eliminating this up-front processing.
To accomplish this, use the azcopy copy command instead, and set the
--overwrite flag to
ifSourceNewer. AzCopy will compare files as they are copied without performing any up-front scans and comparisons. This provides a performance edge in cases where there are a large number of files to compare.
The azcopy copy command doesn't delete files from the destination, so if you want to delete files at the destination when they no longer exist at the source, then use the azcopy sync command with the
--delete-destination flag set to a value of
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