** logstash version **

Logstash 7.x >= 7.17.5
Logstash 8.x >= 8.3.0

Steps to reproduce:

1. Configure multiple pipelines where the total PQ requested is greater than the remaining number of bytes on allocated disk
2. Start logstash

When starting up, Logstash will check the total amount of space required for PQ's on a specified file system against the amount of disk left on that file system, logging a warning when the total amount of space is exceeded.

However, the warning message emitted is difficult to follow and provide the correct remediating action:

I set up a config on my laptop where I have 312Gi free on my local drive, and configured two pipelines, each with

queue.max_bytes: 300gb 

configured and started up logstash.

I received the following warning message:

[2023-01-11T17:43:50,148][WARN ][logstash.persistedqueueconfigvalidator] The persistent queue on path "/Users/robbavey/logstash-8.5.0/data/queue/test" won't fit in file system "/dev/disk1s2" when full. Please free or allocate 643171352576 more bytes. The persistent queue on path "/Users/robbavey/logstash-8.5.0/data/queue/test2" won't fit in file system "/dev/disk1s2" when full. Please free or allocate 643171352576 more bytes. 

This number - Please free or allocate 643171352576 more bytes. - feels a little confusing as I actually need fewer bytes than that to successfully allow the PQ's to operate.

The number appears to
(Total Size of required disk across all PQ) - (disk used across all PQ)

But the disk may not be dedicated to PQ and the number may be misleading.

It may be more useful to report

• the total number of bytes that logstash requires for PQ storage for the specific file system
• the number of bytes actually free on that file system
• the number of bytes being used by PQ on that file system
• the requirements for each PQ on that file system

It may also be worth strengthening the warning to state that Logstash may fail to start if this is not resolved