From: Mike Hartman <mike@hartmanipulation.com>
To: Neil Brown <neilb@suse.de>
Cc: Wolfgang Denk <wd@denx.de>, linux-raid@vger.kernel.org
Subject: Re: How to initialize "composite" RAID
Date: Sat, 11 Sep 2010 01:15:19 -0400 [thread overview]
Message-ID: <AANLkTin1+9UcCbY2DZyTffZW4A2fHzZh-DVCsTxdUq=1@mail.gmail.com> (raw)
In-Reply-To: <20100911150923.41043519@notabene>
On Sat, Sep 11, 2010 at 1:09 AM, Neil Brown <neilb@suse.de> wrote:
> On Sat, 11 Sep 2010 00:58:21 -0400
> Mike Hartman <mike@hartmanipulation.com> wrote:
>
>> > If you add a bitmap (mdadm --grow /dev/md0 --bitmap=internal) after the
>> > current resync finished, then any subsequent resync due to an unclean
>> > shutdown will be much faster.
>>
>> I read somewhere (I think in the wiki) that an intent bitmap only
>> works properly on ext2 and ext3 and can cause trouble on other file
>> systems. Can I use one on ext4 (what I'm using)? I'm hoping/assuming
>> what I read just predates the common use of ext4.
>
> That is completely wrong. An intent bitmap works properly no matter what
> filesystem is on top.
> It does impose a small performance penalty for writes which is very
> work-load-dependant, and it is not impossible that different filesystems
> would suffer more or less from this, but I doubt you would notice.
>
> If you can find it again let me know and I'll try to get it fixed.
I found it. Looks like I misremembered what it said though - it's
referring to external bitmaps only.
In the man page: "Note: external bitmaps are only known to work on
ext2 and ext3. Storing bitmap files on other filesystems may result
in serious problems."
Thanks again!
>
>>
>> Will I need to remove the bitmap before adding another disk and
>> growing the array to use it? If I don't, will it speed up that
>> operation any?
>
> You, you will need to remove the bitmap before growing the array. I really
> should fix that but it doesn't seem to rise to the top of my to-do list...
>
> And no, a bitmap would have no effect on a reshape operation even if it were
> allowed to be present.
>
> NeilBrown
>
>
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next prev parent reply other threads:[~2010-09-11 5:15 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-10 22:14 How to initialize "composite" RAID Mike Hartman
2010-09-10 22:28 ` Wolfgang Denk
2010-09-10 22:33 ` Mike Hartman
2010-09-10 22:37 ` Neil Brown
2010-09-10 22:45 ` Mike Hartman
2010-09-10 23:07 ` Neil Brown
2010-09-10 23:36 ` Mike Hartman
2010-09-11 0:23 ` Neil Brown
2010-09-11 2:30 ` Mike Hartman
2010-09-11 4:42 ` Neil Brown
2010-09-11 4:58 ` Mike Hartman
2010-09-11 5:09 ` Neil Brown
2010-09-11 5:15 ` Mike Hartman [this message]
2010-09-11 22:13 ` John Robinson
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