Re: staggered stripes

[Hugo Mills <hugo@carfax.org.uk>]

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On Thu, May 15, 2014 at 07:00:10PM +1000, Russell Coker wrote:
> http://www.cs.wisc.edu/adsl/Publications/corruption-fast08.html
> 
> Page 13 of the above paper says:
> 
> # Figure 12 presents for each block number, the number of disk drives of disk
> # model ‘E-1’ that developed a checksum mismatch at that block number. We see
> # in the figure that many disks develop corruption for a specific set of block
> # numbers. We also verified that (i) other disk models did not develop
> # multiple check-sum mismatches for the same set of block numbers (ii) the
> # disks that developed mismatches at the same block numbers belong to
> # different storage systems, and (iii) our software stack has no specific data
> # structure that is placed at the block numbers of interest.
> #
> # These observations indicate that hardware or firmware bugs that affect
> # specific sets of block numbers might exist. Therefore, RAID system designers
> # may be well-advised to use staggered stripes such that the blocks that form
> # a stripe (providing the required redundancy) are placed at different block
> # numbers on different disks.
> 
> Does the BTRFS RAID functionality do such staggered stripes?  If not could it 
> be added?

   Yes, it could, by simply shifting around the chunk locations at
allocation time. I'm working in this area at the moment, and I think
it should be feasible within the scope of what I'm doing. I'll add it
to my list of things to look at.

   Hugo.

> I guess there's nothing stopping a sysadmin from allocating an unused 
> partition at the start of each disk and use a different size for each disk.  
> But I think it would be best to do this inside the filesystem.
> 
> Also this is another reason for having DUP+RAID-1.
> 

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
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