From: Andreas Klauer <Andreas.Klauer@metamorpher.de>
To: Ramon Hofer <ramonhofer@bluewin.ch>
Cc: linux-raid@vger.kernel.org
Subject: Re: "bitmap" line in /proc/mdstat
Date: Fri, 14 Oct 2016 16:10:00 +0200 [thread overview]
Message-ID: <20161014141000.GA23227@metamorpher.de> (raw)
In-Reply-To: <5800E4B8.9040205@bluewin.ch>
On Fri, Oct 14, 2016 at 03:59:20PM +0200, Ramon Hofer wrote:
> Still I would imagine if I assume that a bit per chunck is needed and I
> use 128kB chuncks on the 11720662272 blocks of the 12TB RAID5 this is:
> log(11720662272)/log(2) = 34 Bytes
>
> Or am I totally wrong?
It's negligible, a few bytes in the metadata somewhere.
The bitmap has its own size (--bitmap-chunk option). It's fine to set
this to a large value (128MiB, 1GiB, ...). That might help performance
and reduce the bytes required for the bitmap itself (not that it matters).
The main issue is performance impact... it's a tradeoff for additional
bitmap updates each write, or long resync time after a power loss or
similar event.
If performance is not critical (e.g. it's a NAS, not a database)
then you can enable it without worries.
Regards
Andreas Klauer
next prev parent reply other threads:[~2016-10-14 14:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-14 10:06 "bitmap" line in /proc/mdstat Ramon Hofer
2016-10-14 11:53 ` Phil Turmel
2016-10-14 12:32 ` Ramon Hofer
2016-10-14 13:59 ` Ramon Hofer
2016-10-14 14:10 ` Andreas Klauer [this message]
2016-10-14 14:23 ` Ramon Hofer
2016-10-14 16:08 ` Peter Sangas
2016-10-14 16:29 ` Ramon Hofer
2016-10-14 17:32 ` Peter Sangas
2016-10-14 17:38 ` Ramon Hofer
2016-10-14 17:43 ` Andreas Klauer
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