Move Volume

Hello,

You would need to open a support case so they can investigate this.  

Are you also replicating that volume?

typically the issue is on the switch side.  Retransmits, etc...

No, I am not replicating the volume. I have looked at various switch stat's on my force10 switches and I don't see any obvious errors.

Not all errors show up on the switch.  Restranmits, fast retransmits, etc are only seen in the "conversation' not the physical switch.  

Hi Don. I have been wiresharking the communications and noticed one item in the equallogic TCP handshake that is doesn't support. The syn-ack from the equallogic packet is not setting the SACK bit. This will turn off fast restransmits between the ESXi and equallogic box. Is this a setting in the EQL. Granted I am not seeing retransmits but if they do happen they will be inefficient.

Hello,

That isn't correct.  We do support fast retransmits and I see that in the array diag reports often enough to know that it works as expected.

.

You don't have to open a new case for that.   You can mention it to the current case owner.

There is no setting to enable / disable fast retransmits.   Nor do I believe it's a bug, since I've seen them in numerous array diags over the last 10 years I have been with Equallogic.

Have you opened a support case to review the diags for your volume move issue?

Regards,

I did open a support case on this.

I'm pretty confident that the array is not negotiating SACK. I assume I need to open a support case on this? I can send them the wireshark capture showing the 3 way handshake. I can see where ESXi is offering selective acks but the EQL is not so it then negotiates to basic restransmits.

The array I have is not offering selective acks and you can that from the screenshot.

The only options that it is offering is window scaling and timestamps. Could this be a setting somewhere or a bug?

BTW, what firmware are you currently running?

I am running version 7.0.7 (R397085).

On general principle, since there are some important fixes since 7.0.7,  I would suggest you upgrade to 7.1.2 as you next opportunity.

I've been doing some research, you are correct EQL does not support syn-ack, however that is not the same thing as "Fast Retransmits"  is what I've been told.  I'm trying to get more detailed info.

Here's a little snippet that discusses when a Fast Retransmit occurs, and it does not require SYN ACK

At times, it may so happen that a receiver receives a TCP segment with a sequence number higher than the expected one (out of order segments). The receiver then sends an immediate ACK with the Acknowledgement field set to the Sequence number the receiver was expecting. This ACK is a duplicate of an ACK (DupACK) which was sent previously. This is basically done to update the sender with regards to the dropped/missing TCP segments. After receiving 2 DUPACKs, TCP performs a retransmission of that segment without waiting for the retransmission timer to expire .This is called a Fast Retransmit.

Regards,

Don you are correct. Supporting fast retransmits does not require selective acknowledgments. However all packets will have to be retransmitted from the start of the lost packet whereas sack would allow retransmissions of only the lost packets.