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Chapter 5

Domain Filesystem Storage

It is possible to directly export any Linux block device in dom0 to another domain, or

to export ﬁlesystems / devices to virtual machines using standard network protocols

(e.g. NBD, iSCSI, NFS, etc). This chapter covers some of the possibilities.

5.1 Exporting Physical Devices as VBDs

One of the simplest conﬁgurations is to directly export individual partitions from do-

main 0 to other domains. To achieve this use the phy: speciﬁer in your domain

conﬁguration ﬁle. For example a line like

disk = [’phy:hda3,sda1,w’]

speciﬁes that the partition /dev/hda3 in domain 0 should be exported read-write to

the new domain as /dev/sda1; one could equally well export it as /dev/hda or

/dev/sdb5 should one wish.

In addition to local disks and partitions, it is possible to export any device that Linux

considers to be “a disk” in the same manner. For example, if you have iSCSI disks or

GNBD volumes imported into domain 0 you can export these to other domains using

the phy: disk syntax. E.g.:

disk = [’phy:vg/lvm1,sda2,w’]

Warning: Block device sharing

Block devices should typically only be shared between domains in a read-

only fashion otherwise the Linux kernel’s ﬁle systems will get very con-

fused as the ﬁle system structure may change underneath them (having

the same ext3 partition mounted rw twice is a sure ﬁre way to cause ir-

reparable damage)! Xend will attempt to prevent you from doing this

by checking that the device is not mounted read-write in domain 0, and

hasn’t already been exported read-write to another domain. If you want

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Belkin XM Commander Manuale Utente Pagina 27