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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