Drobo Pro (iSCSI) random disconnection (OSX)

I have my Drobo Pro randomly disconnected on me the 2nd time now. When this happens, my mac will display a warning message that said something about not properly ejecting external drive. After a few minutes the Drobo Pro automatically get connected again and everything seems to be fine again.

Nevertheless, I still like to know if anyone had experienced the same issue I had. I have dual disk redundancy turned on, but for an external device to randomly disconnect is still scary. You never know what data could be lost.

My setup is iMac > gigabit switch > Drobo Pro (on static IP, assigned by MAC address on the TimeMachine (router))


Altho the info below are extracted from Microsoft iSCSI Software Initiator Version 2.X Users Guide, the part on networking best practices should still be useful for non-Windows users. We are playing our droboPro on a 1Gig iSCSI segment & so far, so good. No random disconnections yet! Will try jumboframe later this week but b/f that we need to understand how this Smart Volume works.

Networking best practices
• Use non blocking switches and set the negotiated speed on the switches.
• Disable unicast storm control on iSCSI ports. Most switches have unicast storm control disabled by default. If your switch has this enabled, you should disable this on the ports connected to iSCSI hosts and targets to avoid packet loss.
• Enable Flow Control on network switches and adapters; flow control ensures a receiver can make the sender pace its speed and is important in avoiding data loss
• Ensure spanning tree algorithm for detecting loops is turned off; loop detection introduces a delay in making a port become usable for data transfer and may lead to application timeouts
• Segregate SAN and LAN traffic. iSCSI SAN interfaces should be separated from other corporate network traffic (LAN). Servers should use dedicated NICs for SAN traffic. Deploying iSCSI disks on a separate network helps to minimize network congestion and latency. Additionally, iSCSI volumes are more secure when… Segregate SAN & LAN traffic can be separated using port based VLANs or physically separate networks.
• Configure additional Paths for High Availability; use either Microsoft MPIO or MCS (multiple connections per session) with additional NICs in the server to create additional connections to the iSCSI storage array through redundant Ethernet switch fabrics.
• Unbind File and Print Sharing from the iSCSI NIC – on the NICs which connect only to the iSCSI SAN, unbind File and Print Sharing.
• Use Gigabit Ethernet connections for high speed access to storage. Congested or lower speed networks can cause latency issues that disrupt access to iSCSI storage and applications running on iSCSI devices. In many cases, a properly designed IP-SAN can deliver better performance than internal disk drives. iSCSI is suitable for WAN and lower speed implementations including replication where latency and bandwidth are not a concern.
• Use Server class NICs. It is recommended to use NICs which are designed for enterprise networking and storage applications.
• Use CAT6 rated cables for Gigabit Network Infrastructures. For 10Gigabit implementations, Cat-6a or Cat-7 cabling is usually required for use with distances over 55 meters.
• Use Jumbo Frames if supported in your network infrastructure. Jumbo Frames can be used to allow more data to be transferred with each Ethernet transaction and reduce the number of frames. This larger frame size reduces the overhead on both your servers and iSCSI targets. For end to end support, each device in the network needs to support Jumbo frames including the NIC and Ethernet switches.

Thanks rambo,
I’d love to segregate the Drobo Pro from the rest of the network, but like I said, I am using an iMac so such option is not viable. I already use a gigabit switch (unmanaged of course, since it’s for home use) and all cables are cat6. I don’t see any data loss when I ping the Drobo Pro. But for some reason, it disconnects on me randomly. Hope someone have some experience about this…

If you are experiencing dropouts, and Finder is complaining about not ejecting properly, I would be afraid of losing data, an maybe even wiping out at a directory.

I have absolutely no idea what any of the iSCSI settings are, or how to access or control them, but it sounds to me like you experiencing a time-out, perhaps caused by the shared use of the LAN and switch.

I would suggest that you consider moving off of iSCSI and moving to FW800, which should be nearly a fast (if the iMac supports it). I really love having that second, dedicated port on my Mac Pro.

It doesn’t matter how fast it is, if it isn’t reliable!

And send in the Diagnostic file.[hr]

Rambo, I would love to know how to do ANY of that on the Mac, although only the Jumbo frames option would seem to apply in the case of a dedicated port on the Mac Pro. But I don’t know if the Drobopro supports it, or how to configure the mac to use it.

Any clue?

Suite B,
We only have 2 Mac Minis in our test lab but we r in the process of getting an Xserver G5 soon. I hope. Btw, we only deal w/ Microsoft & the big 3 PC/Server manufactures & related hardware. We are more comfortable w/ Windows than dangerous & endangered spicies like the Tiger, Leopard and Snow Leopard! So, no clue until our 1st Apple Xserver & Snow Leopard arrived!

Be careful with the drobopro and the G5 Xserve. I am unable to use iSCSI with my dual G5 Xserve on 10.5.8, it causes an instant kernel panic that support is as of yet unable to reproduce. FW800 performance was pretty dismal (although lately so has been the iSCSI performance on my workstation).

Suite B:

You can adjust the NIC settings in OSX in the System Preferences->Network->(select the interface) and press advanced button in the bottom right. Then select the right-most tab for ethernet. You can adjust both the flow and the MTU in there. Make sure to hit apply after you’ve done changing things. Also if you’re going to move to jumbo frames it’s probably best to power down the drobopro first. Not that you’re likely to lose data or anything, but if you try to force jumbo frames (MTU of 9000) and the drobopro is attached and still trying to use standard frames (MTU 1500) your NIC will just keep going back to standard frames immediately.

Does the drobopro support jumbo frames natively or is there something we have to do in order to enable it on the drobopro?

It is difficult to find information about this. I did not notice a performance improvement when I changed my network card jumbo frame setting from disabled to enabled.

Tks Gerk for the tip but we r getting one anyway cuz the price is irresistable for a slightly slower CPU unit!

Not saying not to get one, just letting you know that YMMV with the drobopro and the Xserve in my experience. I love my Xserve, very solid piece of hardware that has served me well for years.

Thanks for the above discussions. I’ll see to send DR some diagnostic info when I get the chance to. My DroboPro was running perfectly and always on for the first few week with no dropouts. The random drops only occurred recently. I might still stick with iSCSI if I can because compared to FW800, iSCSI still seem to give more performance.

I was wondering if I should be getting a new switch or router that handles gigabit traffics better, and might solve the dropout issue? I am currently using the Apple TimeCapsule as my router and the SMC8508T gigabit switch. Maybe the switch is not good enough? Anyways, if anyone got any ideas, please let me know, thanks.

I’m testing iSCSI w/ my netgear 8-port 1Gig unmanaged switch & so far OK. I have a Cisco/Linksys WRT610N 1Gig router w/ StorageLink at home & I’ll give that a try & provide further updates.

I certainly understand that most computers, and all Macs other than the Mac Pro (and perhaps the Mac server) only have one network port, and for that reason if both Internet connectivity and DroboPro iSCSI connections are required, a router/switch is the only viable option.

However, in the interest of keeping everyone sane while trying to debug some of these problems, I would suggest that people try to replicate whatever problem they are having with the DroboPro connected directly to the Ethernet port, just to eliminate the other variables.

Chasing a problem with one variable is hard enough, but chasing two variables is hard squared.

The Linksys Storage Link only supports FAT32. Even the D-Link DIR-865 latest & greatest N (Draft) router also doesn’t support NTFS (Read/Write). netgear 3700 supports NTFS but the unit has not been released. So, droboShare is still our best NAS option.
Suite B: Hop over to StarWind Software (http://www.StarWindSoftware.com) & check out their iSCSI initiator library. They have published over a dozen of excellent white papers on how iSCSI integrated w/ various WIndows centric NOS including VMware, MSCS etc. Sorry, not much on MacOS or VMware Fusion tho.