grub and bcache

grub and bcache

[James Harper]

Is the underlying bdev bcache format such that bios/grub won't be able to boot off it?

Or to put it another way, I am wondering whether I can get away with:

/dev/sd[ab]
 md0
  bcache
   lvm
    lv-root
    lv-boot

like I do now without bcache and have grub find the lv-boot, or if I need a separate md device to hold /boot like:

/dev/sd[ab]
  md0
    boot
  md1
    bcache
      lvm
        lv-root
        lv-boot

thanks

James

Re: grub and bcache

[Kent Overstreet]

On Sun, Aug 12, 2012 at 11:17:39AM +0000, James Harper wrote:
> Is the underlying bdev bcache format such that bios/grub won't be able to boot off it?

Bios isn't an issue, because the mbr just takes up the first 512 bytes
of the hard drive and bcache leaves the first 4k of the device unused.
But grub needs to be able to read everything, and it doesn't know
anything about bcache devices.

> 
> Or to put it another way, I am wondering whether I can get away with:
> 
> /dev/sd[ab]
>  md0
>   bcache
>    lvm
>     lv-root
>     lv-boot
> 
> like I do now without bcache and have grub find the lv-boot, or if I need a separate md device to hold /boot like:

Yeah, this is the one you'll need.

> 
> /dev/sd[ab]
>   md0
>     boot
>   md1
>     bcache
>       lvm
>         lv-root
>         lv-boot
> 
> thanks
> 
> James
> 
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