Re: [Lsf-pc] [LSF/MM TOPIC] [ATTEND] Future writeback topics

[Boaz Harrosh <bharrosh@panasas.com>]

On 01/22/2012 05:49 PM, James Bottomley wrote:
> 
> But this topic then becomes adding alignment for non block backed
> filesystems?  I take it you're thinking NFS rather than MTD or MMC?
> 

Sorry to differ. But no this is for most making the IO aligned in the first
place. Block-dev or not. Today VFS has no notion of alignment and IO is
submitted as is with out any alignment considerations.

> For multiple devices, you do a simple cascade ... a bit like dm does
> today ... but unless all the devices are aligned to optimal I/O it never
> really works (and it's not necessarily worth solving ... the idea that
> if you want performance from an array of devices, you match
> characteristics isn't a hugely hard one to get the industry to swallow).
> 

No I'm talking about raid configurations like object raid in exofs/NFS or
raid0/5 in BTRFS and ZFS and such, where there are other larger alignment
structures to consider. Also for large-blocks filesystems/devices who
would like IO aligned on bigger than a page sizes.

Thanks
Boaz

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