[gpfsug-discuss] NSD network checksums (nsdCksumTraditional)

Kumaran Rajaram kums at us.ibm.com
Mon Oct 29 19:56:09 GMT 2018


Hi,

>>How can it be that the I/O performance degradation warning only seems to 
accompany the nsdCksumTraditional setting and not GNR?
>>Why is there such a penalty for "traditional" environments?

In GNR IO/NSD servers (ESS IO nodes), the checksums are computed in 
parallel  for a NSD (storage volume/vdisk) across the threads handling 
each pdisk/drive (that constitutes the vdisk/volume). This is possible 
since the GNR software on the ESS IO servers is tightly integrated with 
underlying storage and is aware of the vdisk DRAID configuration 
(strip-size, pdisk constituting vdisk etc.) to perform parallel checksum 
operations. 

In non-GNR + external storage model, the GPFS software on the NSD 
server(s) does not manage the underlying storage volume (this is done by 
storage RAID controllers)  and the checksum is computed serially. This 
would contribute to increase in CPU usage and I/O performance degradation 
(depending on I/O access patterns, I/O load etc).

My two cents.

Regards,
-Kums





From:   Aaron Knister <aaron.s.knister at nasa.gov>
To:     gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date:   10/29/2018 12:34 PM
Subject:        [gpfsug-discuss] NSD network checksums 
(nsdCksumTraditional)
Sent by:        gpfsug-discuss-bounces at spectrumscale.org



Flipping through the slides from the recent SSUG meeting I noticed that 
in 5.0.2 one of the features mentioned was the nsdCksumTraditional flag. 
Reading up on it it seems as though it comes with a warning about 
significant I/O performance degradation and increase in CPU usage. I 
also recall that data integrity checking is performed by default with 
GNR. How can it be that the I/O performance degradation warning only 
seems to accompany the nsdCksumTraditional setting and not GNR? As 
someone who knows exactly 0 of the implementation details, I'm just 
naively assuming that the checksum are being generated (in the same 
way?) in both cases and transferred to the NSD server. Why is there such 
a penalty for "traditional" environments?

-Aaron

-- 
Aaron Knister
NASA Center for Climate Simulation (Code 606.2)
Goddard Space Flight Center
(301) 286-2776
_______________________________________________
gpfsug-discuss mailing list
gpfsug-discuss at spectrumscale.org
http://gpfsug.org/mailman/listinfo/gpfsug-discuss





-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://gpfsug.org/pipermail/gpfsug-discuss_gpfsug.org/attachments/20181029/e47c2a4e/attachment.htm>


More information about the gpfsug-discuss mailing list