[DRBD-user] Performance with DRBD + iSCSI

Weilin Gong wgong at alcatel-lucent.com
Wed Feb 21 23:46:36 CET 2007


Ross S. W. Walker wrote:
>> -----Original Message-----
>> From: drbd-user-bounces at lists.linbit.com 
>> [mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of Weilin Gong
>> Sent: Wednesday, February 21, 2007 1:11 PM
>> Cc: drbd-user at lists.linbit.com
>> Subject: Re: [DRBD-user] Performance with DRBD + iSCSI
>>
>> Ross S. W. Walker wrote:
>>     
>>> You can only write into drbd using what your application 
>>>       
>> can handle and
>>     
>>> for VFS file operations that is 4k io! 
>>>       
>> On Solaris ufs, the "maxcontig" parameter can be tuned to specify the 
>> the number of contiguous
>> blocks written to the disk. Haven't found the equivalence on 
>> Linux yet.
>>     
>
> Well, if you write your own app you can bypass VFS page-memory io
> restriction by using the generic block layer.
>
> I'm not sure if you quite understand the maxcontig parameter either:
>
> maxcontig=n The maximum number of logical
> blocks, belonging to one file, that
> are allocated contiguously. The
> default is calculated as follows...
>
> This parameter is for tuning disk space allocation in order to reduce
> fragmentation, it doesn't affect the io block size.
>   
Actually, this defines the max io data size the file system sends down 
to the driver.
We have a home grown vdisk driver, similar to drbd, the "maxcontig" had 
to be
tuned to match the size of the buffer allocated for the network transport.
> -Ross
>
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