IN THIS ARTICLE
In Qumulo Core 5.0.4 (and higher), you can enable access time updates for file and directory reads (the
access_time timestamp that indicates time of last access). This article describes how you can set access time updates for your entire Qumulo cluster by using the Qumulo CLI.
HOW ACCESS TIME WORKS
This section explains access time functionality.
How Access Time Updates Work
By default, access time is the file creation time (unless a user updates the access time manually or enables access time updates).
When you enable access time updates, read operations on files and directories update the access time value. This includes reads by users with read-only permissions or files and directories accessed through read-only exports. For more information, see the Access Time and Replication section.
All protocols that enable file and directory reads (REST, NFSv3, NFSv4.1, SMB, and FTP) can manipulate access time.
How the Granularity Setting Works
Qumulo Core doesn't update access time on every read.
When you enable access time updates explicitly, every file and directory read updates the access time value before returning the read results if the previous access time is older than the granularity setting (
WEEK) relative to the current time. The default granularity setting is 1 hour.
Consider the following example:
- You have enabled access time updates for your cluster with the
- A file has access time set to
- The current time is
In this example, reading the file updates the access time to the current time. However, subsequent reads update the access time only after
- Because the granularity setting might have a significant performance impact on read workloads, you must consider whether to enable access time updates or, if you enable the feature, how granular its setting should be.
The only exceptions to normal synchronous persistence are situations in which writes aren't possible because the cluster space is fully used, or if the cluster is in a read-only, degraded condition. In such cases, we allow reads to prevent outages.
Access Time and Replication
If a file's access time changes because it was adjusted manually or because of a read, the access time is replicated to the target.
- To maintain point-in-time consistency with the source snapshot, reads on a locked target directory don't update access time.
- Enabling access time updates might increase replication traffic, especially for read-heavy workflows.
- Enabling access time updates together with continuous replication might cause metadata contention. This can impact performance, especially on hybrid clusters or metadata-heavy workloads. To mitigate performance problems in such situations, you can switch to snapshot policy replication.
TO ENABLE ACCESS TIME UPDATES
To enable access time updates (with default one-hour granularity), use the
fs_set_atime_settings CLI command.
$ qq fs_set_atime_settings -e
The configuration of the current cluster and the granularity setting are returned.
To set different granularity, use the
$ qq fs_set_atime_settings -g DAY
You can now set access time updates for your Qumulo cluster.
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