iSCSI Overheads. Are there any?

[Geoff]

I also suggest you look at using DFS to make aliases for your file shares that you can move around independent of the actual file server being used. Microsoft calls this DFS namespaces. You can ignore the replication aspect.

Designing Distributed File Systems

[dhicks]

AoE has been implemented in Linux, along with iSCSI.

You wouldn't happen to know if there a free Windows-XP-based server for AoE, iSCISI, or pretty much any other SAN protocol, would you?

--
David Hicks

[ranj]

Since moving over all of the staff/pupils home directories and profiles to the iSCSI target we have suffered some performance issues. Its not been horrendously slow but there are times when some staff and pupils are saving or opening work on their computers and it will just hang.

Currently at the moment the iscsi initiator and target are connected onto the same switch but effectively on the same network. The network card on the initiator is doing both network traffic and iscsi traffic and I have been told that if we use the second network card on there which doesnt have a TCP offload engine (TOE) it will make a difference and would have to monitor CPU usage and if too high might need to invest in a TOE compatible network card.

I just wanted to get other views on this. If I used the second network card to just do iSCSI traffic will this help. Its currently all connected to a Layer 2 gigabit switch which does support VLans and the rest.

I am currently using Microsoft's ISCSI initator and would really appreciate any recommendations if someone has already performed this at their own institution.

Thanks

[torledo]

Since moving over all of the staff/pupils home directories and profiles to the iSCSI target we have suffered some performance issues. Its not been horrendously slow but there are times when some staff and pupils are saving or opening work on their computers and it will just hang.

Currently at the moment the iscsi initiator and target are connected onto the same switch but effectively on the same network. The network card on the initiator is doing both network traffic and iscsi traffic and I have been told that if we use the second network card on there which doesnt have a TCP offload engine (TOE) it will make a difference and would have to monitor CPU usage and if too high might need to invest in a TOE compatible network card.

I just wanted to get other views on this. If I used the second network card to just do iSCSI traffic will this help. Its currently all connected to a Layer 2 gigabit switch which does support VLans and the rest.

I am currently using Microsoft's ISCSI initator and would really appreciate any recommendations if someone has already performed this at their own institution.

Thanks

Yes, use the second network as a dedicated iscsi initiator.....you've been told right, ToE is only beneficial when you start getting high CPU utilization, and the ToE can unburden the CPU from certain tasks such as iSCSI processing. iSCSI being one example of a protocol that can make good use of ToE.

The idea of using VLANs with iscsi would be to isolate and create a dedicated iSCSI SAN, without employing dedicated gigabit switches for your iSCSI traffic. I'm pretty sure the main reason for your poor performance is the mixing of LAN and iSCSI traffic on the same adapter, not a good idea imo. at the end of the day you want the full bandwidth and processing capability of the adapter for iSCSI use only....and you do want to segment the targets and initiators using VLANs or dedicated gigabit switches.

[diggory]

Since moving over all of the staff/pupils home directories and profiles to the iSCSI target we have suffered some performance issues. Its not been horrendously slow but there are times when some staff and pupils are saving or opening work on their computers and it will just hang.

Currently at the moment the iscsi initiator and target are connected onto the same switch but effectively on the same network. The network card on the initiator is doing both network traffic and iscsi traffic and I have been told that if we use the second network card on there which doesnt have a TCP offload engine (TOE) it will make a difference and would have to monitor CPU usage and if too high might need to invest in a TOE compatible network card.

I just wanted to get other views on this. If I used the second network card to just do iSCSI traffic will this help. Its currently all connected to a Layer 2 gigabit switch which does support VLans and the rest.

I am currently using Microsoft's ISCSI initator and would really appreciate any recommendations if someone has already performed this at their own institution.

Thanks

Another way to improve performance with a seperate VLAN is to change the MTU to a higher rate on the VLAN your SAN system will be on. This help performance of the SAN side of things, as well as having the SAN traffic on a seperate NIC and indeed VLAN.
be wary though, non-matching MTU sizes between your servers can cause issues -which is why it's easier to set on a small VLAN between a small bunch of servers with (hopefully) new NICs.

We used to have a SAN system on the same subnet as the rest of our client and servers etc, with the same NIC on the server being used for SAN and 'normal' traffic.

Then we moved to the SAN traffic being on a seperate NIC on it's own VLAN with increased MTU size (increased on SAN box to match).

Performance was much improved -to be fair we did upgrade the SAN box too.

We currently use the SAN system for storing backups from MS DPM.
But we are about to expand it for user spaces and shared 'drives'
Using Intel SSR212MC2R2 boxes (they'll take most SATA or SAS disks) with openfiler to provide the iSCSI target and the MS Iniiator.