lkml.org 
[lkml]   [2010]   [Mar]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: ATA 4 KiB sector issues.
Date
On Thursday 11 March 2010 18:34:56 Theodore Tso wrote:
> On Mar 10, 2010, at 11:19 AM, Damian Lukowski wrote:
> > I have practically no knowledge of Linux' block device drivers,
> > but is this really a partitioning issue? I think the problem is
> > with the filesystems when clustering multiple blocks without
> > knowledge of the sector alignment and sector size of the underlying
> > block device. Maybe it is a better solution to adapt the filesystem
> > buffer routine which reads/writes data from/to the block device?
>
> No, it's really a partitioning issue. If the paging subsystem wants a 4k
> block to fill a particular page, we need to read that 4k block into
> memory. If we need to swap out that 4k block, we need to write that 4k
> block to swap space, or to the memory segment's backing store. If the
> partition is misaligned by 512 bytes, this is simply not possible. The
> file system has to do what is requested of it by its users, and the
> reality is that we need to do 4k aligned reads and writes with respect to
> the beginning of the partition, far more often than not.
>
> Hence, if we want the best performance on 4k sector drives, the partition
> needs to be aligned with respect to what is most desirable for the device
> in question.
>

I guess, what he meant was, to keep filesystem blocks aligned, even if the
partition is not. Say if the partition is mis-aligned by 512-bytes, let the
filesystem waste 4k-512bytes and keep it's blocks aligned. But it might be a
case of over-engineering, possibly requiring disk format change.

Thanks
Nikanth


\
 
 \ /
  Last update: 2010-03-11 14:59    [W:0.093 / U:0.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site