From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nikolaus Rath <Nikolaus@rath.org>
Subject: Re: How to use multiple backing devices
Date: Tue, 09 Feb 2016 08:03:53 -0800
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	<20160209083847.0cff87c6@jupiter.sol.kaishome.de>
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In-Reply-To: <20160209083847.0cff87c6@jupiter.sol.kaishome.de> (Kai Krakow's
	message of "Tue, 9 Feb 2016 08:38:47 +0100")
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On Feb 09 2016, Kai Krakow <hurikhan77@gmail.com> wrote:
> Am Mon, 08 Feb 2016 20:47:10 -0800
> schrieb Nikolaus Rath <Nikolaus@rath.org>:
>
>> Hello,
>>=20
>> If I'm understanding Documentation/bcache.txt correctly, I should be
>> able to use one SSD to cache multiple spinning disks.
>>=20
>> However, I'm at a loss of how to set this up in practice. I believe =
I
>> need to do
>>=20
>>   make-bcache -B /dev/sda  # spinning rust
>>   make-bcache -B /dev/sdb  # spinning rust=20
>>   make-bcache -C /dev/sdc  # ssd
>>=20
>> and then something like
>>=20
>>   echo <CSET-UUID> > /sys/block/bcacheX/bcache/attach
>>=20
>>=20
>> But what do I have to put for X, and what for CSET-UUID? I believe f=
or
>> at least one of those values I will have two options (because there
>> are two backing devices).
>
> Create it in one go:
>
> make-bcache -C /dev/sdc -B /dev/sd{a,b}
>
> It will take away the hassle. Everything should be setup now.

Yeah, but unfortunately I don't have enough space for that. I need to
create one, move the data over from second, create the second, move dat=
a
over from the SSD, and then create the SSD is caching device.


> But if you want to do it manually: you have to run "echo" twice - for
> each X (the backing devices). CSET-UUID comes from /sys/fs/bcache whe=
re
> you will find a UUID per each bcache caching device, which is just on=
e
> for your case.


Ah, ok. Intuitively attaching the same cache device to two different
backing devices sounds dangerous, but I'll  take your word that the cod=
e
is designed for that...

Thanks,
-Nikolaus

(No Cc on replies please, I'm reading the list)
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