Re: impact of 4k sector size on the IO & FS stack

[Ric Wheeler <ric@emc.com>]

Alan Cox wrote:
>> Are there other concerns in the IO or FS stack that we should bring up 
>> with vendors?  I have been asked to summarize the impact of 4k sectors 
>> on linux  for a disk vendor gathering and want to make sure that I put 
>> all of our linux specific items into that summary...
>>     
>
> We need to make sure the physical sector size is correctly reported by
> the disk (eg in the ATA7 identify data) but I think for libata at least
> the right bits are already there and we've got a fair amount of scsi disk
> experience with other media sizes (eg 2K) already. 256byte/sector media
> is still broken btw 8)
>   
It would be really interesting to see if we can validate this with 
prototype drives.
> I would be interested to know what the disk vendors intend to use as
> their strategy when (with ATA) they have a 512 byte write from an older
> file system/setup into a 4K block. The case where errors magically appear
> in other parts of the fs when such an error occurs are not IMHO too well
> considered.
>
> Alan
As Jeff mentioned, I think that they would have to do a 
read-modify-write simulation which would kill performance for a small, 
random write work load...

ric