block size question

block size question

[Vlad]

Hallo,

What would be the optimal block size in case if physical block sizes
different for cache and backing devices? Can I use different block sizes
for cache and backing devices, like:
make-bcache --block 4k -B /dev/sdc
make-bcache --block 512 -C /dev/sda

I have a feeling that the block size should be the same and the biggest
block size should be used, but I'd appreciate any thoughts about that.

Thanks in advance,
Vlad.

Re: block size question

[Killian De Volder]

The blocksize should be equal or bigger then the blocking device.
Otherwise you risk writing multiple blocks 512 for 1 1k sector, resulting in read-modify-write transaction on 4k disks.

But for some reason I didn't do this on my desktop.
(I might need to reformat if i'm right about this :( )


Killian De Volder
On 18-05-16 07:50, Vlad wrote:
> Hallo,
> 
> What would be the optimal block size in case if physical block sizes
> different for cache and backing devices? Can I use different block sizes
> for cache and backing devices, like:
> make-bcache --block 4k -B /dev/sdc
> make-bcache --block 512 -C /dev/sda
> 
> I have a feeling that the block size should be the same and the biggest
> block size should be used, but I'd appreciate any thoughts about that.
> 
> Thanks in advance,
> Vlad.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bcache" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: block size question

[Killian De Volder]

PS you wish to use the real sector size of the SSD if applicaple according to make-bache -?
-w, --block		block size (hard sector size of SSD, often 2k

This also implies you should set the block-size of a backing device to 4K.

Killian De Volder


On 18-05-16 07:50, Vlad wrote:
> Hallo,
> 
> What would be the optimal block size in case if physical block sizes
> different for cache and backing devices? Can I use different block sizes
> for cache and backing devices, like:
> make-bcache --block 4k -B /dev/sdc
> make-bcache --block 512 -C /dev/sda
> 
> I have a feeling that the block size should be the same and the biggest
> block size should be used, but I'd appreciate any thoughts about that.
> 
> Thanks in advance,
> Vlad.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bcache" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: block size question

[Killian De Volder]

Done some testing for you:
The -B --block size has to be a a power2 of -C --block size.

(Note: all information is about bcache1 not bcachefs if that is what you are talking about)

Killian De Volder


On 18-05-16 07:50, Vlad wrote:
> Hallo,
> 
> What would be the optimal block size in case if physical block sizes
> different for cache and backing devices? Can I use different block sizes
> for cache and backing devices, like:
> make-bcache --block 4k -B /dev/sdc
> make-bcache --block 512 -C /dev/sda
> 
> I have a feeling that the block size should be the same and the biggest
> block size should be used, but I'd appreciate any thoughts about that.
> 
> Thanks in advance,
> Vlad.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bcache" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: block size question

[Vlad]

Killian,

Thanks for your help! I think it's the best to reformat both bcache
devices with block size of 4k in my case where cached device has block
size of 512 and backing device 4k.

Regards,
Vlad.

On 18/05/16 17:46, Killian De Volder wrote:
> Done some testing for you:
> The -B --block size has to be a a power2 of -C --block size.
>
> (Note: all information is about bcache1 not bcachefs if that is what you are talking about)
>
> Killian De Volder
>
>
> On 18-05-16 07:50, Vlad wrote:
>> Hallo,
>>
>> What would be the optimal block size in case if physical block sizes
>> different for cache and backing devices? Can I use different block sizes
>> for cache and backing devices, like:
>> make-bcache --block 4k -B /dev/sdc
>> make-bcache --block 512 -C /dev/sda
>>
>> I have a feeling that the block size should be the same and the biggest
>> block size should be used, but I'd appreciate any thoughts about that.
>>
>> Thanks in advance,
>> Vlad.
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-bcache" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bcache" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html