From 7427e581f1b8450224ccc3af94db71eda4cd6a6f Mon Sep 17 00:00:00 2001 From: "kaf24@scramble.cl.cam.ac.uk" Date: Sat, 8 Jan 2005 17:30:16 +0000 Subject: [PATCH] bitkeeper revision 1.1159.170.83 (41e018a8GZXpwMHfGSHGmgyM2JmjSQ) Doc update from John Griffin. --- docs/src/user.tex | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/docs/src/user.tex b/docs/src/user.tex index f098260378..3b9d3773ca 100644 --- a/docs/src/user.tex +++ b/docs/src/user.tex @@ -981,6 +981,7 @@ chapter covers some of the possibilities. \section{Exporting Physical Devices as VBDs} +\label{s:exporting-physical-devices-as-vbds} One of the simplest configurations is to directly export individual partitions from domain 0 to other domains. To @@ -1074,8 +1075,23 @@ In the configuration file set: As the virtual machine writes to its `disk', the sparse file will be filled in and consume more space up to the original 2GB. +{\bf Note that file-backed VBDs may not be appropriate for backing +I/O-intensive domains.} File-backed VBDs are known to experience +substantial slowdowns under heavy I/O workloads, due to the I/O handling +by the loopback block device used to support file-backed VBDs in dom0. +Better I/O performance can be achieved by using either LVM-backed VBDs +(Section~\ref{s:using-lvm-backed-vbds}) or physical devices as VBDs +(Section~\ref{s:exporting-physical-devices-as-vbds}). + +Linux supports a maximum of eight file-backed VBDs across all domains by +default. This limit can be statically increased by using the {\em +max\_loop} module parameter if CONFIG\_BLK\_DEV\_LOOP is compiled as a +module in the dom0 kernel, or by using the {\em max\_loop=n} boot option +if CONFIG\_BLK\_DEV\_LOOP is compiled directly into the dom0 kernel. + \section{Using LVM-backed VBDs} +\label{s:using-lvm-backed-vbds} A particularly appealing solution is to use LVM volumes as backing for domain file-systems since this allows dynamic -- 2.30.2