The backup runs on the same server as the sites, and every megabyte it keeps on disk is space the customer doesn’t get.
How much space does the backup engine’s local cache take per account, and what happens if it is deleted?
Result
~30 MBof cache for 233,612 files, about 130 bytes per file
18 sfor an incremental run with the cache deleted, versus 19 s with a full cache; with no cache at all, 76 s
Why it matters to whoever runs the server
Server disk: 30 MB of cache for 233 thousand files is little next to an account of several GB. And since the cache is deleted when each account finishes, the server doesn’t pile up caches for hundreds of accounts.
Time: deleting the cache didn’t slow the incremental down (18 s with it deleted, 19 s with it full). No cache at all makes the backup 4× slower (76 s): a longer backup window, with the sites sharing the server for longer.
Incremental backup time for one account233,612 files, 5.7 GB · lower is better
Full cache
19 s
Cache deleted first
18 s
No cache
76 s
Source: Salvo Lab · cPanel test server · Oct 14, 2026
See the data as a table
Run
Time
Peak memory
First backup, empty repository
53 s
842 MB
Incremental, full cache
19 s
168 MB
Incremental, cache deleted first
18 s
169 MB
Incremental, no cache
76 s
133 MB
Method
A cPanel test server (CentOS 7, 18 cores, internal network to the storage) and one account with 233,612 files and 5.7 GB, in its own repository.
Salvo engine, writing over SFTP, with encrypted data.
Low priority (nice -n 19, ionice -c3); the test would stop on its own if server load went above 9.
What we decided
The cache is now temporary: it is created when an account’s backup starts and deleted when it ends, and the server only keeps cache for the accounts being backed up at that moment (implemented on Oct 15, 2026, running on test servers). Running with no cache at all is not worth it: the backup becomes four times slower.
?
What we don’t know yetIn the incremental runs the files were already in system memory (the Linux page cache). A real next-day backup, before dawn and with an empty cache, was measured later: 4 s for 21 thousand files (Lab 12). And this was a single account: memory with several accounts in parallel was measured in Lab 08.
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