Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Does anyone have any ideas what could cause the secondary node to use smaller IO, or anyway to debug the problem?
Thanks,
Chris
-----Original Message-----
From: Pascal BERTON [mailto:pascal.berton3 at free.fr]
Sent: Friday, June 10, 2011 10:16 PM
To: Gouveia, Chris; drbd-user at lists.linbit.com
Subject: RE: [DRBD-user] Secondary server works harder than primary
Hello Chris!
Ok, these numbers make more sense, your platform is sane. However this shows something very interesting about what's happening under the cover : The IO profile is different on both side, the destination issuing smaller IOs. In order to get something optimized, I'd rather expect the IO size information on primary side being transmitted to the secondary one in order to achieve "equal" things, unfortunately I don't have enough DRBD knowledge to tell if that's something one might act upon. If it turned to be impossible, the underliying disk technology and cache would then probably have a significant impact in terms of latencies, especially in C policy. Especially if one was to use it for virtualization which is known to be a bigger disk stresser than traditional contexts. I give hand to the DRBD experts now, just let's wait for what they think about that... Maybe there's some magic parameter that would allow us to make things go better. Anyhow, that's an interesting point, good to know!
Best regards,
Pascal.
-----Message d'origine-----
De : drbd-user-bounces at lists.linbit.com
[mailto:drbd-user-bounces at lists.linbit.com] De la part de Chris.Gouveia at spirent.com Envoyé : samedi 11 juin 2011 01:50 À : drbd-user at lists.linbit.com Objet : [DRBD-user] Secondary server works harder than primary
Thank you for your reply. Enclosed are more accurate and consistent results:
Primary machine
avg-cpu: %user %nice %system %iowait %steal %idle
0.16 0.00 1.19 15.70 0.00 82.94
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 37.33 24.00 985.33 72 2956
sdb 34.67 21.33 954.67 64 2864
sdd 40.33 16.00 950.67 48 2852
md0 729.33 61.33 2890.67 184 8672
Secondary machine
avg-cpu: %user %nice %system %iowait %steal %idle
0.04 0.00 0.28 0.00 0.00 99.68
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 194.00 0.00 978.67 0 2936
sdb 199.67 0.00 990.67 0 2972
sdc 191.33 0.00 948.00 0 2844
md0 734.00 0.00 2916.00 0 8748
Would it be accurate to interpret that DRBD is issuing the same number of requests to both servers, but for whatever reason the software RAID on the secondary server is breaking up each request into smaller IO requests?
If so, would anyone have any suggestions on how to debug the software RAID portion?
Thanks for everyone's time,
Chris Gouveia
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