Three limits appear on most hosting plans and they behave completely differently. Confusing them leads to buying the wrong upgrade.
Disk space
Total storage used by everything: website files, databases, mail, logs and backups. It is a level, not a rate — you either fit or you do not.
When space runs out, symptoms are strange rather than obvious. Sites throw database errors because the database cannot write. Mail is rejected. Uploads fail silently. If several unrelated things break at once, check disk space before anything else.
The usual hidden consumers, in order: old mailboxes nobody reads, backups stored on the same account they are backing up, and log files that were never rotated.
Bandwidth
The volume of data transferred out over a billing period. It is a rate, and it resets.
An unexpected spike is rarely more customers. It is usually one large file being downloaded repeatedly, a bot crawling the site aggressively, or an image hotlinked from a busy third-party page. Check the traffic statistics in your control panel before assuming you need a bigger plan — a single rule blocking the source often solves it for nothing.
Inodes
The one nobody expects. An inode is a filesystem entry: one per file, one per directory. The limit is on the count, not the size. Half a million tiny files can exhaust an inode limit while using a fraction of the disk allowance.
When you hit the limit, you cannot create files even though the space meter shows room. That includes session files and cache files, so the site frequently stops working entirely.
The offenders are almost always: a cache directory that was never cleared, a mail queue full of failed delivery notices, and framework session files that accumulate because the cleanup task was never scheduled. Deleting a cache directory's contents typically recovers tens of thousands of inodes in seconds.
Working out what is actually using the space
Most control panels include a disk usage viewer that breaks usage down by directory. Start at the top and follow the largest number down. Do this before deleting anything.
When an upgrade is the right answer
Upgrade when the usage is real and growing: a genuinely larger site, more mailboxes, more visitors. Do not upgrade to escape a runaway log file or an unclosed cache directory, because the new plan will fill too, only later and more expensively.
If you are unsure which of the three you are hitting, send us the figures from your control panel and we will tell you.
