Last week I built my vSphere Home Lab "The Green Machines". One of the biggest purchases I made for my lab was the Synology DS411+. I bought this NAS because DSM 3.0 is supposed to be "VMware Ready" and it has NFS, iSCSI, and iSCSI Thin Provisioning abilities. During my testing with iSCSI, I noticed some unusual behavior. If i ever put an I/O load on iSCSI, the connection to the VMware ESXi servers would drop off. It wasn't heavy I/O either, the connection would drop during an install of Office 2010 on my Windows 7 VM. The datastore on ESXi would gray out and go italic, but the NFS datastore was still available. I am running the latest DSM 3.0 Build 1372.
To remedy the situation, I would have to go back in to the Synology GUI, restart the iSCSI service, reboot the NAS, then reboot both of my ESXi servers and it was back. I did a quick google search which lead me to this post on the Synology forums ESX 4 and iSCSI problem. This was the same exact symptoms I saw so I opened up a ticket with Synology and sent them my log file. Luckily, they knew the exact problem and already have an undocumented remedy.
Here was the response:
Hello Kendrick,
Thank you for that information. You were right, the relevant errors were at the top of the debug file. Thank you for that. I would like to recommend downgrading the iSCSI target engine to IET from LIO in order to try to resolve the issue you are experiencing. The attached patch will downgrade the iSCSI engine on the DiskStation, you can install it by going to DiskStation Manager > Control Panel > DSM update.
The reason for downgrading is that sometimes compatibility issues can arise using the newer LIO engine, so downgrading to IET should resolve the issue you are experiencing.
While the update is not designed to affect your data in any way, I always like to be over-cautious and recommend backing up before performing any changed to the DSM software.
Please let me know the results.
Best Regards,
Roger F.
Synology America Corp.
Here is the file: iscsi_downgrade.pat
After downgrading the iSCSI controller, rebooting the NAS and rebooting my ESXi hosts, I was able to install Office 2010 without any problems.
