A beginner project

[Eric Anderson]

On 01/22/07 01:12, Shane Adams wrote:
> I've thought about geom snapshots, which I take it you would do at a block layer similarly to how snapshots are implemented in FFS.  I couldnt figure out a way to do it effeciently.  I've found the FFS snapshots do not work well with large disk sets, there is a noticable lag and almost a freeze-up on my computer.  
> 
> Seems you'd need to do it at the filesystem layer, and as a side effect change the format of inodes at cylinder groups in order to track changes.
> 
> Is there any publish literature on the subject?
> 
> Oh - by snapshot I mean something that can be mounted simlultaniously with the original filesystem.


I don't think this could work at all like UFS snapshots, since those are 
based on using the cylinder groups to make a virtual vopy of the file 
system structure.

To me, I would think that one would could implement it in a number of 
ways, not sure which is best.  One idea is to supply the device to 
snapshot, and then also the location of a snapshot file to be created. 
The snapshot file would be created via COW, and could be a sparse file.

One side effect could be the creation of another new geom layer - geom 
union.  So, you can take something like a disk, and overlay an image on 
top, and the result would be blocks that exist in the overlay are seen, 
and blocks that are not in the overlay are transparent and the next 
layer down is visible.

Eric



> ----- Original Message ----
> From: Eric Anderson <anderson at centtech.com>
> To: Soeren Straarup <xride at x12.dk>
> Cc: freebsd-geom at freebsd.org
> Sent: Sunday, January 21, 2007 10:16:22 PM
> Subject: Re: A beginner project
> 
> On 01/20/07 01:31, Soeren Straarup wrote:
>> What would be a beignner project within geom?
>>
>> Something is acutally going to be used by atleat some.
>>
>> I have briefly looked at:
>> http://www.freebsd.org/projects/ideas/#p-psched
>>
>> But are there already someone out there that is working on it?
>>
>> /Soeren
>>
> 
> Make a 'geom taste' function?
> 
> Other ideas:
> - geom snapshots (harder!)
> - gnop additional options (add latency, etc, to mimic real devices)
> 
> 
> Eric
> 
> 
> 


-- 
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Eric Anderson        Sr. Systems Administrator        Centaur Technology
An undefined problem has an infinite number of solutions.
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