BUG REPORT: ReadyNAS can't RSYNC with jumbo frames enabled

[Nima304]

Hello,

I wasn't really sure where to post this, so please move if this isn't the right section.

I am running a ReadyNAS Pro 6, ReadyNAS 102, and 314. The ReadyNAS 102 and 314 are running OS6.2.4, the Pro6 is running 6.2.2. All are affected by this issue. I backup from the Pro6 to the 314 nightly, and from the 314 to the 102 weekly. Because of our large backup sizes, we went to jumbo frames (9000 MTU), which gave us a 10-15% increase in transfer speeds. However, somewhere along the line, this started causing us issues, which caused months of pain and suffering, and caused us to replace one of our NAS servers twice.

The issues were that RSYNC would connect, but would hang and timeout after 1802 seconds. Here is the full error:

[Receiver] io timeout after 1802 seconds -- exiting
rsync error: timeout in data send/receive (code 30) at io.c(195) [Receiver=3.1.1]

I checked network connectivity, DNS, NTP, permissions, matched /etc/passwd and /etc/shadow, backup settings, everything. I tried running RSYNC manually between the servers, nothing seemed to work. It would simply hang and not transfer any data. However, other servers could transfer data to the NAS servers just fine using RSYNC, which didn't make any sense to me at the time.

Finally, I switched the MTUs back to default, and everything worked. Those servers that could RSYNC to the NASes had 1500 MTUs on their interfaces, disabling jumbo frames, allowing them to communicate. Somewhere in the ReadyNAS, something doesn't like jumbo frames. Not sure where it is, but hopefully someone somewhere can fix it. If not, hopefully others with this issue can find this thread and implement a fix.

You could say that this issue could be caused by an unsupported box running OS6, but jumbo frames worked fine at 9000 MTU when we had three OS4 boxes backing up nightly.

[mdgm-ntgr]

Perhaps one or more of your devices does not support a MTU of 9000. You could try a lower MTU.

[Nima304]

mdgm wrote:
Perhaps one or more of your devices does not support a MTU of 9000. You could try a lower MTU.

I've already solved the problem by going to the default MTU of 1500. We don't have a dedicated lab for testing, so I can't confirm if it is a hardware issue or not, but it doesn't make much sense given that MTUs are a software construct.

[mdgm-ntgr]

Jumbo Frames support depends on the router/switch and each of the devices that will be using it. The implementation can be quite different from one device to the next and some devices will support Jumbo Frames over a MTU of 9000 whilst others will only support a MTU that is less than that.

[StephenB]

Nima304 wrote:
...MTUs are a software construct...

No they aren't. The largest packet size that can be sent over the connection might depend on software limits, but more usually there is a hardware or network constraint that limits the size.