How to get best performance from iSCSI between Virtual Host and Guest

iscsivirtualizationvmware-serverwindows-server-2008

I am using iSCSI to connect to some hard drives on the host from a guest.

Here is my setup:

Vmware Server 2 on host
Windows Server 2008 (host and guest)
StarWind Enterprise iSCSI target on host
MS iSCSI initiator on the guest

The guest only has one network adaptor – setup in bridged mode from the host.

With this out-of-box configuration I am getting about 10 MB/s. I know the physical disks are capable of at least 50MB/s.

Any tips for better performance?

Best Answer

iSCSI doesn't respond well to shared network scenarios (where iSCSI traffic has to contend with general purpose traffic for the machine). It might help to create a dedicated connection for iSCSI traffic only - add another virtual Nic to the Guest, connect it to VMnet1 (the Host-Only Virtual Switch), set up your iSCSI Target Software to use the address on the Host-Only Virtual NIC within the host OS and reconfigure the iSCSI initiator to connect to the new Target address.

Your scenario will add a fair amount of CPU overhead - you should expect a couple of hundred Mhz additional load within the guest and a similar additional load in the host just from the iSCSI and virtual networking traffic.

Make sure you have VMWare tools installed. It improves the network stack significantly and the virtual disk subsystem within the guest.

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Problem removing iSCSI target from ESXi 4.0 host

I don't understand why you're only able to use 1TB but I suspect it's due to ESX/i's 2TB-per-LUN limit - basically you can't have a single VMFS extent larger than 2TB nor can it address a larger than 2TB LUN properly - carve your iSCSI LUNs into <2TB and try that again.

As for the problem you face, well if ESXi doesn't 'see' it then you're safe to do what you like from the LaCie perspective - i.e. reboot it as it appears to still be locked. This may just be an incompatibility issue, no LaCie storage products are on the VMWare Hardware Compatibility List I'm afraid.

ISCSI performance between SAN and hypervisor horribly slow

You should see a significant increase of performance after enabling write caching on the target (details depends on the implementation - what are you using, tgt?) and your disks

hdparm -W 1 /dev/sda
hdparm -W 1 /dev/sdb

There is a price however: this will endanger data integrity (especially if you run databases) in the case of a power outage or a system hang of the SAN, as data which is thought to have been permanently written to disk, only resided in volatile DRAM. To mitigate this risk, you should use a controller with BBWC (battery-backed write cache) where data would survive a power outage for a while (typically 1-2 days).

The main "problem" with ESXi is that it is constantly sync()ing the disks. The need to write metadata to VMFS (if you have it) makes it even worse. The vmware community forums are full of "my disks are slow" posts whenever people are using controllers without write caches.

Best Answer

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