I/O caching under QEMU KVM virtualization on Linux

Caching modes in QEMU

Mode Host page cache Guest disk write cache
none off on
writethrough on off
writeback on on
unsafe on ignored

Considerations

  • device.virtio-disk0.config-wce=off (qemu) or config-wce=off (libvirt) prevents guest from setting the write cache
  • Use cache=none for local RAW storage, cache=writethrough for NFS/iSCSI backed storage

TELUS VDSL2 modems deployed in the field

Actiontec V1000H

Specifications

Hardware

Board ID Broadcom 96368VVW
Memory 64MB
Flash 32MB (AM29LV320MT)
Ethernet 5 Ports (1 WAN)
Wireless 802.11 (b, g, n)
HPNA Yes
USB Yes

Software

Release 31.30L.48
Kernel Linux 2.6.21.5
Build Date Wed Sep 1 23:33:32 PDT 2010

Alcatel Cellpipe 7130 (TELUS 3Ve.A2010TEL)

Specifications

Hardware

Board ID Broadcom 96368MVWGV11
Memory 64MB
Flash 4MB (MX29LV320AB)
Ethernet 1 Port
Wireless No
HPNA No
USB No

Software

Release TJ3-65-014E
Kernel Linux 2.6.21.5
Build Date Wed Dec 30 09:12:42 CST 2009