From: Pavel Machek <pavel@ucw.cz>
To: Theodore Ts'o <tytso@mit.edu>,
Reindl Harald <h.reindl@thelounge.net>,
linux-ext4@vger.kernel.org,
kernel list <linux-kernel@vger.kernel.org>,
kent.overstreet@gmail.com, linux-bcache@vger.kernel.org
Subject: Re: bcache with existing ext4 filesystem
Date: Tue, 25 Jul 2017 08:43:04 +0200 [thread overview]
Message-ID: <20170725064304.GA11723@amd> (raw)
In-Reply-To: <20170725045156.kbyaxj4mmi75yyt5@thunk.org>
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On Tue 2017-07-25 00:51:56, Theodore Ts'o wrote:
> On Mon, Jul 24, 2017 at 10:04:51PM +0200, Pavel Machek wrote:
> > Question for you was... Is the first 1KiB of each ext4 filesystem still
> > free and "reserved for a bootloader"?
>
> Yes.
Thanks.
> > If I needed more for bcache superblock (8KiB, IIRC), would that be
> > easy to accomplish on existing filesystem?
>
> Huh? Why would the bcache superblock matter when you're talking about
> the ext4 layout? The bcache superblock will be on the bcache
> device/partition, and the ext4 superblock will be on the ext4
> device/partition.
I'd like to enable bcache on already existing ext4 partition. AFAICT
normal situation, even on the backing device, is:
| 8KiB bcache superblock | 1KiB reserved | ext4 superblock | 400GB data |
Unfortunately, that would mean shifting 400GB data 8KB forward, and
compatibility problems. So I'd prefer adding bcache superblock into
the reserved space, so I can have caching _and_ compatibility with
grub2 etc (and avoid 400GB move):
| 1KiB (modified) bcache superblock | ext4 superblock | 400GB data |
Best regards,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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next prev parent reply other threads:[~2017-07-25 6:43 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-24 18:57 bcache with existing ext4 filesystem Pavel Machek
2017-07-24 19:08 ` Reindl Harald
2017-07-24 19:15 ` Pavel Machek
2017-07-24 19:27 ` Theodore Ts'o
2017-07-24 20:04 ` Pavel Machek
2017-07-25 4:51 ` Theodore Ts'o
2017-07-25 6:43 ` Pavel Machek [this message]
2017-07-25 10:32 ` Vojtech Pavlik
2017-07-25 11:12 ` Pavel Machek
2017-07-25 16:10 ` Theodore Ts'o
2017-07-25 18:13 ` Eric Wheeler
2017-07-25 22:02 ` Pavel Machek
2017-07-26 17:41 ` Eric Wheeler
2017-07-26 18:59 ` Austin S. Hemmelgarn
2017-07-26 19:16 ` Eric Wheeler
2017-07-26 20:01 ` Pavel Machek
2017-07-25 13:46 ` Pavel Machek
2017-07-25 18:02 ` Theodore Ts'o
2017-07-25 20:55 ` Pavel Machek
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