From: Marc Lehmann <schmorp@schmorp.de>
To: Hugo Mills <hugo@carfax.org.uk>, linux-btrfs@vger.kernel.org
Subject: Re: questoin about Data=single on multi-device fs
Date: Mon, 27 Apr 2020 13:29:47 +0200 [thread overview]
Message-ID: <20200427112946.GA3648@schmorp.de> (raw)
In-Reply-To: <20200426102547.GM32577@savella.carfax.org.uk>
On Sun, Apr 26, 2020 at 11:25:47AM +0100, Hugo Mills <hugo@carfax.org.uk> wrote:
> > The reason I chose data=single was specifically to help in case of device
> > loss at the cost of performance.
>
> Make backups. That's the only way to be sure about this sort of thing.
I think you are unthinkingly repeating a wrong (and slightly dangerous)
claim - backups cannot actually do that sort of thing: a raid will protect
against (some amount of) disk failures with no data loss, but backups
cannot: Backups can protect against complete data loss, but cannot
completely protect against data loss.
> With single data, *chunk allocation* will go to the device with the
> largest amount of unallocated space. If your data is WORM
That is definitely not the case with 5.4 - I added two disks to an
existing filesystem and copied 8TB onto it with btrfs receive, resulting
in about 3800G used on both new disks, with Data=single. I repeated it by
creating a 5 disk-fs and 1TB of data and got prettyx even distribution.
--
The choice of a Deliantra, the free code+content MORPG
-----==- _GNU_ http://www.deliantra.net
----==-- _ generation
---==---(_)__ __ ____ __ Marc Lehmann
--==---/ / _ \/ // /\ \/ / schmorp@schmorp.de
-=====/_/_//_/\_,_/ /_/\_\
next prev parent reply other threads:[~2020-04-27 11:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-26 10:04 questoin about Data=single on multi-device fs Marc Lehmann
2020-04-26 10:25 ` Hugo Mills
2020-04-27 11:29 ` Marc Lehmann [this message]
2020-04-27 11:44 ` Roman Mamedov
2020-04-27 12:32 ` Marc Lehmann
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200427112946.GA3648@schmorp.de \
--to=schmorp@schmorp.de \
--cc=hugo@carfax.org.uk \
--cc=linux-btrfs@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).