Re: [Xen-users] Xen + Storage

[Tom Fritz <tfritz@xxxxxxxxx>]

>    i have 4 debian squeeze with xen 4 and all them with 4 to 6 HVM virtual 
> machines. All the VMs are located in a fith machine (A SuperMicro LSI 
> Controller as storage).
>    The host servers are Intel i7 with 24GB fo RAM (Debian Squeeze + Xen4) 
> and the storage a Xen 3.0 with 8GB of RAM (CentOS 5.5 + TGTD) and thery are 
> all connect with a gigabit network dedicated for the iSCSI.
>    My problem is, when working at the storage, doing backup procedures with 
> the command dd and using the bzip2, the IOWait increases a litle bit, the 
> normal state is close to 0%, but when copying or moving the files generated 
> by the backup, usually bigger than 2G, the IOWait increases too much, 
> reaching 100%, in cases in all 4 cores, making the virtual machines stop 
> responding and even if i stop the procedure, the virtual machines doesnt 
> comes back, been necessary a reboot or shutdown.
>    Does anyone knows about this problem ? And there is any configuration 
> that i could do in the iSCSI-Target and Initiator to increase de performance? 
> And a configuration in the virtual machines filesystem to prevent it from 
> stopping?
	I always use ionice when using dd to do a backup. You should also 
look into scst-iscsi. The default for most distro's is the IET iscsi.
Cheers,

Tom.

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