From: "Fabian Grünbichler" <f.gruenbichler@proxmox.com>
To: Proxmox VE user list <pve-user@lists.proxmox.com>
Subject: Re: [PVE-User] PBS : is dirty-bitmap really accurate ?
Date: Thu, 23 Jul 2020 08:43:06 +0200 [thread overview]
Message-ID: <1595486387.pi9zv7y79a.astroid@nora.none> (raw)
In-Reply-To: <1110267368.76036.1595436034847.JavaMail.zimbra@fws.fr>
On July 22, 2020 6:40 pm, Daniel Berteaud wrote:
> Hi
>
> 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 ?
possibly you haven't upgraded to pve-qemu-kvm 5.0-11 (or your VM hasn't
been restarted yet since the upgrade):
https://git.proxmox.com/?p=pve-qemu.git;a=commit;h=f257cc05f4fbf772cad3231021b3ce7587127a1b
the bitmap has a granularity of 4MB, so depending on the activity inside
you can see quite a bit of amplification. also writing and then
zeroing/reverting again to the old content would leave a mark in the
bitmap without permanently changing the contents.
next prev parent reply other threads:[~2020-07-23 6:43 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-22 16:40 Daniel Berteaud
2020-07-23 6:43 ` Fabian Grünbichler [this message]
2020-07-23 6:53 ` Daniel Berteaud
2020-07-23 9:00 ` Jorge Boncompte
2020-07-23 9:34 ` Fabian Grünbichler
2020-07-23 9:40 ` Daniel Berteaud
2020-07-23 21:59 ` Roland
2020-07-24 7:02 ` Daniel Berteaud
2020-07-24 7:54 ` Ronny Aasen
2020-07-26 9:24 ` Mark Schouten
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