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Re: [dm-devel] [Lsf-pc] [LSF/MM TOPIC] a few storage topics



On 2012-01-25, at 7:00 AM, Jan Kara wrote:
> On Wed 25-01-12 14:35:52, Wu Fengguang wrote:
>> On Tue, Jan 24, 2012 at 11:15:13PM -0700, Andreas Dilger wrote:
>>> I'm all in favour of 1MB (aligned) readahead.
>> 
>> 1MB readahead aligned to i*1MB boundaries? I like this idea. It will
>> work well if the filesystems employ the same alignment rule for large
>> files.
> 
> Yeah. Clever filesystems (e.g. XFS) can be configured to align files e.g.
> to raid stripes AFAIK so for them this could be worthwhile.

Ext4 will also align IO to 1MB boundaries (from the start of LUN/partition)
by default.  If the mke2fs code detects the underlying RAID geometry (or the
sysadmin sets this manually with tune2fs) it will store this in the superblock
for the allocator to pick a better alignment.

Cheers, Andreas







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