Michael Monnerie
2009-Jan-17 08:42 UTC
[Xen-users] Double amount of READ DISK traffic on dom0 than from domU?
Dear list, did anybody of you see a similar behaviour? I have a test server with a single XEN VM running. In it, there''s a PostgreSQL DB running a CLUSTER command, which basically copies the table in a new order. The domU VM said it''s 35MB/s read and 35MB/s write, but the dom0 said it''s about TWICE the amount on *read* only (79MB/s read, 35MB/s write). The command with which I watched was iostat -kx 5 555 on both domU and dom0. The values were most of the time nearly exaclty domU-reads * 2 = dom0-reads. Writes were the same numbers both in domU and dom0. Of course the values vary a bit because the iostat command doesn''t run exactly at the same time in domU and dom0, but I watched a long time and it''s about twice as much reads on dom0. I would understand the other way round, that could be because of caching in dom0, but this results are strange. Anybody got an explanation? Real Server dom0: Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util sda 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 sdb 0,00 1,80 10254,40 231,80 79640,00 40258,40 22,87 1,16 0,11 0,04 46,96 XEN VM domU: Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util xvda 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 xvdb 0,00 0,00 839,92 0,00 35794,01 0,00 85,23 4,90 5,83 1,18 99,00 xvdc 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 xvdd 0,00 0,00 0,00 821,36 0,00 35823,55 87,23 51,17 61,97 1,21 99,48 Later I tested again: Real Server dom0: Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util sda 0,00 0,20 0,00 0,40 0,00 2,40 12,00 0,00 0,00 0,00 0,00 sdb 0,20 0,00 3246,31 68,66 24988,42 7826,75 19,80 0,38 0,11 0,07 24,43 XEN VM domU: Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util xvda 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 xvdb 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 xvdc 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 xvdd 0,00 0,40 277,84 365,27 11681,44 15674,65 85,07 26,68 41,49 0,83 53,49 -- // Michael Monnerie, Ing.BSc ----- http://it-management.at // Tel: 0660 / 415 65 31 .network.your.ideas. // PGP Key: "curl -s http://zmi.at/zmi.asc | gpg --import" // Fingerprint: AC19 F9D5 36ED CD8A EF38 500E CE14 91F7 1C12 09B4 // Keyserver: wwwkeys.eu.pgp.net Key-ID: 1C1209B4 _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users