[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
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