Re: btrfs support for efficient SSD operation (data blocks alignment)

[Liu Bo <liubo2009@cn.fujitsu.com>]

On 02/09/2012 03:24 AM, Martin wrote:
> My understanding is that for x86 architecture systems, btrfs only allows
> a sector size of 4kB for a HDD/SSD. That is fine for the present HDDs
> assuming the partitions are aligned to a 4kB boundary for that device.
> 
> However for SSDs...
> 
> I'm using for example a 60GByte SSD that has:
> 
>     8kB page size;
>     16kB logical to physical mapping chunk size;
>     2MB erase block size;
>     64MB cache.
> 
> And the sector size reported to Linux 3.0 is the default 512 bytes!
> 
> 
> My first thought is to try formatting with a sector size of 16kB to
> align with the SSD logical mapping chunk size. This is to avoid SSD
> write amplification. Also, the data transfer performance for that device
> is near maximum for writes with a blocksize of 16kB and above. Yet,
> btrfs supports a 4kByte page/sector size only at present...
> 
> 
> Is there any control possible over the btrfs filesystem structure to map
> metadata and data structures to the underlying device boundaries?
> 
> For example to maximise performance, can the data chunks and the data
> chunk size be aligned to be sympathetic to the SSD logical mapping chunk
> size and the erase block size?
> 

The metadata buffer size will support size larger than 4K at least, it is on development.

> What features other than the trim function does btrfs employ to optimise
> for SSD operation?
> 

e.g COW(avoid writing to one place multi-times),
delayed allocation(intend to reduce the write frequency)

thanks,
liubo

> 
> Regards,
> Martin
> 
> 
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