[PVE-User] PBS : is dirty-bitmap really accurate ?

Daniel Berteaud daniel at firewall-services.com
Wed Jul 22 18:40:34 CEST 2020


I've started playing with PBS on some VM. So far, it's looking really promizing. 
There's one strange thing though : the percent of the dirty data. For example, I backup one VM every 2 or 3 days. It's a moderately busy server, mainly serving a MariaDB database (zabbix server + mariadb). On each backup, I get similar dirty values : 

INFO: using fast incremental mode (dirty-bitmap), 492.7 GiB dirty of 590.0 GiB total 

While I'm sur not even 10% of this has really been written. 

Get more or less the same problem on other VM. One which I know just sleep all day (my personnal OnlyOffice document server), and which I backup daily, and get values like : 

INFO: using fast incremental mode (dirty-bitmap), 5.0 GiB dirty of 10.0 GiB total 

Or another small one (personnal samba DC controler) : 

INFO: using fast incremental mode (dirty-bitmap), 13.0 GiB dirty of 20.0 GiB total 

The only write activity for those 2 are just a few KB or maybe MB of log lines. Respectivly 5 and 13GB of dirty blocks seems unreal. 

Am I the only one seeing this ? Could the dirty-bitmap mark dirty blocks without write activity somehow ? 



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Daniel Berteaud 
FIREWALL-SERVICES SAS, La sécurité des réseaux 
Société de Services en Logiciels Libres 
Tél : +33.5 56 64 15 32 
Matrix: @dani:fws.fr 
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