Synology iSCSI NAS becomes innactive with VMware ESXi sessions over time

Posted on 2016-09-19
Last Modified: 2016-09-28
I have noticed in the past few months as I've been settling my system in (getting everything configured right and all) that my Synology NAS which is hosting an iSCSI volume randomly appears to "disconnect" from certain hosts.  I put that in quotes as the Synology UI still shows the host as connected however the host displays that the SCSI route is dead in the network adapters page and the volume is inactive.  Upon attempting to shut down the NAS I am left with powercycling using a hard boot.  A power cycle of the NAS is the only option as rebooting the host does not reestablish a connection.  Any ideas?
Question by:huntson
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LVL 121
ID: 41805393
does the host lose contact to the NAS, e.g. network connection?

what does vmkping or ping tell you ?

is your Synology NAS certified for use with ESXi, e.g. on the HCL

we've had lots of bad experiences with Synology NAS, and use only NFS now for Backup, not production, e.g. iSCSI.

Author Comment

ID: 41805472
Not sure how I can answer your question specifically other than telling you it thinks the route is bad. Vmkping shows that the host is seeing the NAS.  

My NAS is certified.  Interesting to hear that considering many people are able to use it successfully.  Any advice for troubleshooting as it only appears to be happening on this one NAS (i have several).  I was thinking about migrating everything off and recreating the disk.
LVL 121
ID: 41805485
if you have networking issues, constant vmkpings and pings, and look at VMware ESXi logs /var/logs

check networking.

is this only one LUN which is causing issues, any other LUNs present ?

do you have jumbo frames enabled ?

are you using multipath ?
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Author Comment

ID: 41805492
What is the best way to do an indefinite ping?
LVL 121
ID: 41805528
vmkping is better because you can specify a vmkernel portgroup to send the "iSCSI data packet"

Author Comment

ID: 41805610
How do I keep that going with vmkping?
LVL 121
ID: 41805642

followed by a number for packet count.


-c 1024

Open in new window


Author Comment

ID: 41805644
FYI this is exactly my issue - not sure if it'll get solved without downgrading:
LVL 121
ID: 41805985
again compatibility issue!

don't use iSCSI!

Accepted Solution

huntson earned 0 total points
ID: 41812847
I see where you're coming from but I loose some compatibility and ability to do certain things if I do it all as NFS - don't I?

Apparently the solution was to add


at the end of


Do this by telneting in and elevating to sudo.  I also changed the max SCSI connections to 256 in the advanced settings of my client as this was a suggestion for my issue however I'm not sure if that's have any impact
LVL 121
ID: 41812852
What do you lose if you use NFS ?

NFS has less overhead on the NAS, because it's designed around NFS, iSCSI adds additional layer, and CPU overhead, Synology processors are not that fast, and they do not have dedicated storage processors!

Author Comment

ID: 41812862
So I can migrate and do all that fun stuff just like iSCSI?
LVL 121
ID: 41812881
VMware vSphere ESXi supports NFS.

If you've not tried NFS and Jumbo Frames, you may find a performance increase.

It's worth trying...(less overhead).

Author Closing Comment

ID: 41819443
I emailed tech support and found the solution.

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