CloudLinux limits how fast each account can read and write to disk. The IO limit caps throughput (MB per second) and IOPS caps the number of disk operations per second. Normal browsing rarely comes close, but backups, imports and some plugins can, and then the whole site slows down.
Before you start
- cPanel access to the account.
- The time when the site felt slow.
Spot IO faults
- Go to cPanel → Metrics → Resource Usage and open Details.
- Look at the IO and IOPS graphs. Usage reaching the limit line is a fault.
- Check the times: faults at night often match a backup plugin; faults during the day match imports or admin actions.
Reading these graphs is covered in Resource Usage.
What hitting the IO limit feels like
- Pages load slowly but without errors; the account is throttled, not stopped.
- The admin area hangs during a backup or import.
- Cron jobs take much longer than usual.
Common causes
| Cause | Fix |
|---|---|
| Backup plugins zipping the whole site | Rely on MdmHost's daily JetBackup backups, or schedule plugin backups at night and exclude caches |
| Large CSV or product imports | Import in smaller batches |
| Regenerating thumbnails for thousands of images | Run in batches; use offloaded optimisation (QUIC.cloud) |
| Plugins writing logs or statistics on every visit | Disable verbose logging, use lighter statistics |
| Huge numbers of small cache files | Use LiteSpeed Cache instead of file-based page cache plugins |
Tip: Image optimisation with LiteSpeed Cache runs on QUIC.cloud servers, not on your account, which avoids heavy local disk work (see the image optimisation guide).
Use the right backup approach
MdmHost already takes daily backups you can restore with JetBackup (see restoring files with JetBackup). Extra backup plugins are optional; if you use one, send backups off-site and skip cache and backup folders.
When to upgrade
If IO faults appear during normal traffic after you have removed heavy tasks, the site may need a larger plan. Resellers can raise IO limits for customers in CloudLinux Manager (see limits for resellers).
For process and memory faults instead, see 508 errors and memory limit errors.
Frequently asked questions
Is IO the same as disk space?
No. IO is speed of reading and writing; disk space is how much you can store, set by your quota.
Does MySQL count towards IO?
Database reads and writes count towards the account's limits too, through MySQL Governor on CloudLinux servers.
How do I find which plugin causes disk load?
Disable suspected plugins one at a time during a quiet period and watch the IO graph, or use X-Ray where available to see slow file operations.
Why are faults at the same time every night?
That is almost always a scheduled backup, cache preload or cron task. Move it, make it lighter or remove it.
Are NVMe disks affected by IO limits?
Yes. The limit is per account regardless of disk type; NVMe makes the server faster overall, but each account still has its share.