From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: zedlryqc@server53.web-hosting.com, linux-btrfs@vger.kernel.org
Subject: Re: Feature requests: online backup - defrag - change RAID level
Date: Mon, 9 Sep 2019 11:51:58 +0800 [thread overview]
Message-ID: <5e6a9092-b9f9-58d2-d638-9e165d398747@gmx.com> (raw)
In-Reply-To: <20190908225508.Horde.51Idygc4ykmhqRn316eLdRO@server53.web-hosting.com>
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On 2019/9/9 上午10:55, zedlryqc@server53.web-hosting.com wrote:
> Hello everyone!
>
[...]
>
> 1) Full online backup (or copy, whatever you want to call it)
> btrfs backup <filesystem name> <partition name> [-f]
> - backups a btrfs filesystem given by <filesystem name> to a partition
> <partition name> (with all subvolumes).
Why not just btrfs send?
Or you want to keep the whole subvolume structures/layout?
>
> - To be performed by creating a new btrfs filesystem in the destination
> partition <partition name>, with a new GUID.
I'd say current send/receive is more flex.
And you also needs to understand btrfs also integrates volume
management, thus it's not just <partition name>, you also needs RAID
level and things like that.
> - All data from the source filesystem <filesystem name> is than copied
> to the destination partition, similar to how RAID1 works.
> - The size of the destination partition must be sufficient to hold the
> used data from the source filesystem, otherwise the operation fails. The
> point is that the destination doesn't have to be as large as source,
> just sufficient to hold the data (of course, many details and concerns
> are skipped in this short proposal)
All can be done already by send/receive, although at subvolume level.
Please check if send/receive is suitable for your use case.
[...]
>
> 2) Sensible defrag
> The defrag is currently a joke. If you use defrag than you better not
> use subvolumes/snapshots. That's... very… hard to tolerate. Quite a
> necessary feature. I mean, defrag is an operation that should be
> performed in many circumstances, and in many cases it is even
> automatically initiated. But, btrfs defrag is virtually unusable. And,
> it is unusable where it is most needed, as the presence of subvolumes
> will, predictably, increase fragmentation by quite a lot.
>
> How to do it:
> - The extents must not be unshared, but just shuffled a bit. Unsharing
> the extents is, in most situations, not tolerable.
I definitely see cases unsharing extents makes sense, so at least we
should let user to determine what they want.
>
> - The defrag should work by doing a full defrag of one 'selected
> subvolume' (which can be selected by user, or it can be guessed because
> the user probably wants to defrag the currently mounted subvolume, or
> default subvolume). The other subvolumes should than share data (shared
> extents) with the 'selected subvolume' (as much as possible).
What's wrong with current file based defrag?
If you want to defrag a subvolume, just iterate through all files.
>
> - I think it would be wrong to use a general deduplication algorithm for
> this. Instead, the information about the shared extents should be
> analyzed given the starting state of the filesystem, and than the
> algorithm should produce an optimal solution based on the currently
> shared extents.
Please be more specific, like giving an example for it.
>
> Deduplication is a different task.
>
> 3) Downgrade to 'single' or 'DUP' (also, general easy way to switch
> between RAID levels)
>
> Currently, as much as I gather, user has to do a "btrfs balance start
> -dconvert=single -mconvert=single
> ", than delete a drive, which is a bit ridiculous sequence of operations.
>
> Can you do something like "btrfs delete", but such that it also
> simultaneously converts to 'single', or some other chosen RAID level?
That's a shortcut for chunk profile change.
My first idea of this is, it could cause more problem than benefit.
(It only benefits profile downgrade, thus only makes sense for
RAID1->SINGLE, DUP->SINGLE, and RAID10->RAID0, nothing else)
I still prefer the safer allocate-new-chunk way to convert chunks, even
at a cost of extra IO.
Thanks,
Qu
>
> ## I hope that you will consider my suggestions, I hope that I'm helpful
> (although, I guess, the short time I spent working with btrfs and
> writing this mail can not compare with the amount of work you are
> putting into it). Perhaps, teams sometimes need a different perspective,
> outsiders perspective, in order to better understand the situation.
>
> So long!
>
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next prev parent reply other threads:[~2019-09-09 3:52 UTC|newest]
Thread overview: 111+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-09 2:55 Feature requests: online backup - defrag - change RAID level zedlryqc
2019-09-09 3:51 ` Qu Wenruo [this message]
2019-09-09 11:25 ` zedlryqc
2019-09-09 12:18 ` Qu Wenruo
2019-09-09 12:28 ` Qu Wenruo
2019-09-09 17:11 ` webmaster
2019-09-10 17:39 ` Andrei Borzenkov
2019-09-10 22:41 ` webmaster
2019-09-09 15:29 ` Graham Cobb
2019-09-09 17:24 ` Remi Gauvin
2019-09-09 19:26 ` webmaster
2019-09-10 19:22 ` Austin S. Hemmelgarn
2019-09-10 23:32 ` webmaster
2019-09-11 12:02 ` Austin S. Hemmelgarn
2019-09-11 16:26 ` Zygo Blaxell
2019-09-11 17:20 ` webmaster
2019-09-11 18:19 ` Austin S. Hemmelgarn
2019-09-11 20:01 ` webmaster
2019-09-11 21:42 ` Zygo Blaxell
2019-09-13 1:33 ` General Zed
2019-09-11 21:37 ` webmaster
2019-09-12 11:31 ` Austin S. Hemmelgarn
2019-09-12 19:18 ` webmaster
2019-09-12 19:44 ` Chris Murphy
2019-09-12 21:34 ` General Zed
2019-09-12 22:28 ` Chris Murphy
2019-09-12 22:57 ` General Zed
2019-09-12 23:54 ` Zygo Blaxell
2019-09-13 0:26 ` General Zed
2019-09-13 3:12 ` Zygo Blaxell
2019-09-13 5:05 ` General Zed
2019-09-14 0:56 ` Zygo Blaxell
2019-09-14 1:50 ` General Zed
2019-09-14 4:42 ` Zygo Blaxell
2019-09-14 4:53 ` Zygo Blaxell
2019-09-15 17:54 ` General Zed
2019-09-16 22:51 ` Zygo Blaxell
2019-09-17 1:03 ` General Zed
2019-09-17 1:34 ` General Zed
2019-09-17 1:44 ` Chris Murphy
2019-09-17 4:55 ` Zygo Blaxell
2019-09-17 4:19 ` Zygo Blaxell
2019-09-17 3:10 ` General Zed
2019-09-17 4:05 ` General Zed
2019-09-14 1:56 ` General Zed
2019-09-13 5:22 ` General Zed
2019-09-13 6:16 ` General Zed
2019-09-13 6:58 ` General Zed
2019-09-13 9:25 ` General Zed
2019-09-13 17:02 ` General Zed
2019-09-14 0:59 ` Zygo Blaxell
2019-09-14 1:28 ` General Zed
2019-09-14 4:28 ` Zygo Blaxell
2019-09-15 18:05 ` General Zed
2019-09-16 23:05 ` Zygo Blaxell
2019-09-13 7:51 ` General Zed
2019-09-13 11:04 ` Austin S. Hemmelgarn
2019-09-13 20:43 ` Zygo Blaxell
2019-09-14 0:20 ` General Zed
2019-09-14 18:29 ` Chris Murphy
2019-09-14 23:39 ` Zygo Blaxell
2019-09-13 11:09 ` Austin S. Hemmelgarn
2019-09-13 17:20 ` General Zed
2019-09-13 18:20 ` General Zed
2019-09-12 19:54 ` Austin S. Hemmelgarn
2019-09-12 22:21 ` General Zed
2019-09-13 11:53 ` Austin S. Hemmelgarn
2019-09-13 16:54 ` General Zed
2019-09-13 18:29 ` Austin S. Hemmelgarn
2019-09-13 19:40 ` General Zed
2019-09-14 15:10 ` Jukka Larja
2019-09-12 22:47 ` General Zed
2019-09-11 21:37 ` Zygo Blaxell
2019-09-11 23:21 ` webmaster
2019-09-12 0:10 ` Remi Gauvin
2019-09-12 3:05 ` webmaster
2019-09-12 3:30 ` Remi Gauvin
2019-09-12 3:33 ` Remi Gauvin
2019-09-12 5:19 ` Zygo Blaxell
2019-09-12 21:23 ` General Zed
2019-09-14 4:12 ` Zygo Blaxell
2019-09-16 11:42 ` General Zed
2019-09-17 0:49 ` Zygo Blaxell
2019-09-17 2:30 ` General Zed
2019-09-17 5:30 ` Zygo Blaxell
2019-09-17 10:07 ` General Zed
2019-09-17 23:40 ` Zygo Blaxell
2019-09-18 4:37 ` General Zed
2019-09-18 18:00 ` Zygo Blaxell
2019-09-10 23:58 ` webmaster
2019-09-09 23:24 ` Qu Wenruo
2019-09-09 23:25 ` webmaster
2019-09-09 16:38 ` webmaster
2019-09-09 23:44 ` Qu Wenruo
2019-09-10 0:00 ` Chris Murphy
2019-09-10 0:51 ` Qu Wenruo
2019-09-10 0:06 ` webmaster
2019-09-10 0:48 ` Qu Wenruo
2019-09-10 1:24 ` webmaster
2019-09-10 1:48 ` Qu Wenruo
2019-09-10 3:32 ` webmaster
2019-09-10 14:14 ` Nikolay Borisov
2019-09-10 22:35 ` webmaster
2019-09-11 6:40 ` Nikolay Borisov
2019-09-10 22:48 ` webmaster
2019-09-10 23:14 ` webmaster
2019-09-11 0:26 ` webmaster
2019-09-11 0:36 ` webmaster
2019-09-11 1:00 ` webmaster
2019-09-10 11:12 ` Austin S. Hemmelgarn
2019-09-09 3:12 webmaster
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