Re: size limit for backing store? block sizes? ("[sdx] Bad block number requested")

[Kai Krakow <hurikhan77@gmail.com>]

Am Tue, 14 Feb 2017 12:05:48 +0100
schrieb "Jens-U. Mozdzen" <jmozdzen@nde.ag>:

> Hi *,
> 
> Zitat von Eric Wheeler <bcache@lists.ewheeler.net>:
> > On Wed, 8 Feb 2017, Kai Krakow wrote:
> > [...]  
> >> What I meant is "make-bcacke --block X". It defaults to X=512b. I
> >> think you may want to force it to 4k and see if your problem
> >> persists.  
> >
> > Maybe --block 4096 should be default in make-bcache?
> >
> > Kent, is there any reason this wouldn't be a good idea?  
> 
> actually, make-bcache seems not to default to 512 octets. If no  
> specific block size is specified on the command line, it determines  
> the maximum sector size of the devices involved:
> 
> --- cut here ---
> if (!block_size) {
> 		for (i = 0; i < ncache_devices; i++)
> 			block_size = max(block_size,
> 					 get_blocksize(cache_devices[i]));
> 
> 		for (i = 0; i < nbacking_devices; i++)
> 			block_size = max(block_size,
> 					 get_blocksize(backing_devices[i]));
> }
> --- cut here ---
> 
> get_blocksize() queries the logical block size as reported by the  
> device ( ioctl(fd, BLKSSZGET, &logical_block_size) ).
> 
> At least that's what I see at  
> https://github.com/g2p/bcache-tools/blob/master/make-bcache.c, said
> to be from Apr 16, 2014. And it seems to be the reason why invoking  
> "make-bcache -B ... -C ..." did create a proper setup for me, while  
> separating that to "make-bcache -B ..." and "make-bcache -C ..."  
> created a wrongly set up caching device for me (backing device has
> 4k sector size, caching device 512b).

The call to max() in this function clearly tells that both devices
(backing and cache) should use the same block size.

I still wonder why attaching different block-sized devices wasn't
denied for you. When I tried it once, it didn't work.

-- 
Regards,
Kai

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