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From: Andrei Borzenkov <arvidjaar@gmail.com>
To: webmaster@zedlx.com, linux-btrfs@vger.kernel.org
Subject: Re: Feature requests: online backup - defrag - change RAID level
Date: Tue, 10 Sep 2019 20:39:45 +0300
Message-ID: <610e9567-2f17-c7c3-01aa-0e1215be44d0@gmail.com> (raw)
In-Reply-To: <20190909131108.Horde.64FzJYflQ6j0CbjYFLqBEz0@server53.web-hosting.com>

09.09.2019 20:11, webmaster@zedlx.com пишет:
...
>>
>> Forgot to mention this part.
>>
>> If your primary objective is to migrate your data to another device
>> online (mounted, without unmount any of the fs).
> 
> This is not the primary objective. The primary objective is to produce a
> full, online, easy-to-use, robust backup. But let's say we need to do
> migration...
>>
>> Then I could say, you can still add a new device, then remove the old
>> device to do that.
> 
> If the source filesystem already uses RAID1, then, yes, you could do it,

You could do it with any profile.

> but it would be too slow, it would need a lot of user intervention, so
> many commands typed, so many ways to do it wrong, to make a mistake.
> 

It requires exactly two commands - one to add new device, another to
remove old device.

> Too cumbersome. Too wastefull of time and resources.
> 

Do you mean your imaginary full backup will not read full filesystem?
Otherwise how can it take less time and resources?

>> That would be even more efficient than LVM (not thin provisioned one),
>> as we only move used space.
> 
> In fact, you can do this kind of full-online-backup with the help of
> mdadm RAID, or some other RAID solution. It can already be done, no need
> to add 'btrfs backup'.
> 
> But, again, to cumbersome, too inflexible, too many problems, and, the
> user would have to setup a downgraded mdadm RAID in front and run with a
> degraded mdadm RAID all the time (since btrfs RAID would be actually
> protecting the data).
> 
>> If your objective is to create a full copy as backup, then I'd say my
>> new patchset of btrfs-image data dump may be your best choice.
> 
> It should be mountable. It should be performed online. Never heard of
> btrfs-image, i need the docs to see whether this btrfs-image is good
> enough.
> 
>> The only down side is, you need to at least mount the source fs to RO
>> mode.
> 
> No. That's not really an online backup. Not good enough.
> 
>> The true on-line backup is not that easy, especially any write can screw
>> up your backup process, so it must be done unmounted.
> 
> Nope, I disagree.
> 
> First, there is the RAID1-alike solution, which is easy to perform (just
> send all new writes to both source and destination). It's the same thing
> that mdadm RAID1 would do (like I mentioned a few paragraphs above).
> But, this solution may have a performance concern, when the destination
> drive is too slow.
> 
> Fortunately, with btrfs, an online backup is easier tha usual. To
> produce a frozen snapshot of the entire filesystem, just create a
> read-only snapshot of every subvolume (this is not 100% consistent, I
> know, but it is good enough).
> 
> But I'm just repeating myself, I already wrote this in the first email.
> 
> So, in conclusion I disagree that true on-line backup is not easy.
> 
>> Even btrfs send handles this by forcing the source subvolume to be RO,
>> so I can't find an easy solution to address that.
> 
> This is a digression, but I would say that you first make a temporary RO
> snapshot of the source subvolume, then use 'btrfs send' on the temporary
> snapshot, then delete the temporary snapshot.
> 
> Oh, my.
> 
> 


  reply index

Thread overview: 111+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-09  2:55 zedlryqc
2019-09-09  3:51 ` Qu Wenruo
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 [this message]
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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