ia64/xen-unstable

changeset 3397:47678d2c18c3

bitkeeper revision 1.1159.170.83 (41e018a8GZXpwMHfGSHGmgyM2JmjSQ)

Doc update from John Griffin.
author kaf24@scramble.cl.cam.ac.uk
date Sat Jan 08 17:30:16 2005 +0000 (2005-01-08)
parents 1c0155635933
children 53666c56e533 470434865778
files docs/src/user.tex
line diff
     1.1 --- a/docs/src/user.tex	Sat Jan 08 17:18:44 2005 +0000
     1.2 +++ b/docs/src/user.tex	Sat Jan 08 17:30:16 2005 +0000
     1.3 @@ -981,6 +981,7 @@ chapter covers some of the possibilities
     1.4  
     1.5  
     1.6  \section{Exporting Physical Devices as VBDs} 
     1.7 +\label{s:exporting-physical-devices-as-vbds}
     1.8  
     1.9  One of the simplest configurations is to directly export 
    1.10  individual partitions from domain 0 to other domains. To 
    1.11 @@ -1074,8 +1075,23 @@ In the configuration file set:
    1.12  As the virtual machine writes to its `disk', the sparse file will be
    1.13  filled in and consume more space up to the original 2GB.
    1.14  
    1.15 +{\bf Note that file-backed VBDs may not be appropriate for backing
    1.16 +I/O-intensive domains.}  File-backed VBDs are known to experience
    1.17 +substantial slowdowns under heavy I/O workloads, due to the I/O handling
    1.18 +by the loopback block device used to support file-backed VBDs in dom0.
    1.19 +Better I/O performance can be achieved by using either LVM-backed VBDs
    1.20 +(Section~\ref{s:using-lvm-backed-vbds}) or physical devices as VBDs
    1.21 +(Section~\ref{s:exporting-physical-devices-as-vbds}).
    1.22 +
    1.23 +Linux supports a maximum of eight file-backed VBDs across all domains by
    1.24 +default.  This limit can be statically increased by using the {\em
    1.25 +max\_loop} module parameter if CONFIG\_BLK\_DEV\_LOOP is compiled as a
    1.26 +module in the dom0 kernel, or by using the {\em max\_loop=n} boot option
    1.27 +if CONFIG\_BLK\_DEV\_LOOP is compiled directly into the dom0 kernel.
    1.28 +
    1.29  
    1.30  \section{Using LVM-backed VBDs}
    1.31 +\label{s:using-lvm-backed-vbds}
    1.32  
    1.33  A particularly appealing solution is to use LVM volumes 
    1.34  as backing for domain file-systems since this allows dynamic