Home / server / Questions / 709007
In Process
basin
Asked: 2015-07-29 02:03:55 +0800 CST

Force disk cache even if guest uses direct i/o

  • 772

Have IBM db2 on Rhel on Hyper-V on Windows Server. The *.vhdx file is on CSV. e.g. C:\ClusterStorage\volume1\hyper-v\oktest-lb1\oktest-lb1.vhdx.

db2 uses O_DIRECT flag (uncached i/o) for its database files, and a small block size 8k or less for read/write operations.

Somehow this direct flag is propagated through the whole stack to the host system. The host cache is not used.

The network lag kills performance of such small operations. tested with dd with oflag=direct / iflag=direct

  • bs=8k: 12Mbytes/s
  • bs=64k: 100Mbytes/s

Need a workaround.

performance

0 Answers