[Pvfs2-developers] [PATCH] modify twod-stripe's default params and add some documentation

[Sam Lang]

Having it work with default parameters doesn't necessarily mean making  
those default parameters exactly like simple stripe.  Our best all  
around solution is to fix this bug with a simple check in the 2d code  
and set the default parameters to something reasonable for a 2d  
distribution in the general case.  We looked at this last year and  
decided that num_groups=2 and striping factor = 256 were reasonable,  
maybe they're not, but it doesn't make sense to make them identical to  
the simple stripe dist.
-sam

On Jul 1, 2008, at 8:08 PM, Rob Ross wrote:

> I agree that it's best to have it work for everyone with default  
> parameters.
>
> -- Rob
>
> On Jul 1, 2008, at 4:15 PM, "Kyle Schochenmaier"  
> <kschoche at gmail.com> wrote:
>
>> We should use simple stripe in that case, which is why i have it
>> defaulted to it now, someone was playing with twod-dist today and
>> noticed that it defaults to having 2 groups, which causes errors when
>> you run it on only a single server.   I would much rather have the
>> defaults allow the distribution to work on *any* setup, rather than
>> just a n>1 servers setup.
>>
>> Its not particularly useful, but I belive it is the right thing to  
>> do,
>> maybe I'm wrong?
>> (the original default settings are worthless for my applications so I
>> have to change them anyhow)
>>
>> Kyle
>>
>> On Tue, Jul 1, 2008 at 4:04 PM, Sam Lang <slang at mcs.anl.gov> wrote:
>>>
>>> Kyle,
>>>
>>> How is this patch useful for you guys?  With a single server (and  
>>> only one
>>> stripe), it doesn't matter what the factor and num_groups are,  
>>> does it?  It
>>> still behaves the same as simple-stripe in that case.  With  
>>> multiple servers
>>> setting the factor and num_groups to 1 does make the 2d  
>>> distribution act
>>> like simple-stripe, but why not just use simple stripe in that case?
>>>
>>> -sam
>>>
>>>
>>> On Jul 1, 2008, at 3:19 PM, Kyle Schochenmaier wrote:
>>>
>>>> Patch is against cvs head, and modifies the default num_groups to  
>>>> be 1
>>>> and the group_strip_factor = 1  so twod-stripe's defaults still  
>>>> work
>>>> when you use it on a single-server, it will now by default behave  
>>>> the
>>>> same as simple-stripe until the user modifies the num_groups and
>>>> strip_factor xattrs.
>>>>
>>>> Also added a brief description of the definitions for the  
>>>> dist_params
>>>> in twod-stripe.
>>>>
>>>> Tested fully functional on my servers.
>>>>
>>>> Kyle
>>>>
>>>>
>>>> Index: src/io/description/dist-twod-stripe.c
>>>> ===================================================================
>>>> RCS file: /anoncvs/pvfs2/src/io/description/dist-twod-stripe.c,v
>>>> retrieving revision 1.5
>>>> diff -r1.5 dist-twod-stripe.c
>>>> 6a7,15
>>>>>
>>>>> /* twod-stripe will take all of the servers in the filesystem and
>>>>> * partition them into num_groups groups.  Data will then be  
>>>>> striped to
>>>>> * each group before we move onto the next group.  The  
>>>>> strip_factor will
>>>>> * determine how many chunks of strip_size are written to each  
>>>>> server
>>>>> * in each group before we transition to the next group.
>>>>> * The striping on the group level is done round-robin in the same
>>>>> * fashion as simple-stripe
>>>>> */
>>>>>
>>>>
>>>>
>>>> Index: include/pvfs2-dist-twod-stripe.h
>>>> ===================================================================
>>>> RCS file: /anoncvs/pvfs2/include/pvfs2-dist-twod-stripe.h,v
>>>> retrieving revision 1.4
>>>> diff -r1.4 pvfs2-dist-twod-stripe.h
>>>> 17c17
>>>> < #define PVFS_DIST_TWOD_STRIPE_DEFAULT_GROUPS 2
>>>> ---
>>>>>
>>>>> #define PVFS_DIST_TWOD_STRIPE_DEFAULT_GROUPS 1
>>>>
>>>> 19c19
>>>> < #define PVFS_DIST_TWOD_STRIPE_DEFAULT_FACTOR 256
>>>> ---
>>>>>
>>>>> #define PVFS_DIST_TWOD_STRIPE_DEFAULT_FACTOR 1
>>>>
>>>>
>>>> -
>>>> Kyle Schochenmaier
>>>> <twod-dist.patch>_______________________________________________
>>>> Pvfs2-developers mailing list
>>>> Pvfs2-developers at beowulf-underground.org
>>>> http://www.beowulf-underground.org/mailman/listinfo/pvfs2- 
>>>> developers
>>>
>>>
>>
>>
>>
>> -- 
>> Kyle Schochenmaier
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