Talk to me about switches and iSCSI

[Oaktech]

Here's the deal.

 

With last years budget I bought 2 servers and a 17tb lenovo s2200 enclosure with the idea of creating a failover cluster. I've gone through the cluster validation wizard and it complains that the iSCSI connections can't talk to one another even though they are on the same network segment. Of course, this is because they are direct attach between the servers and the enclosure.

 

For validation to work, I need switches to put between the servers and the enclosure. Obviously 10GBE switches are quite expensive, even more so because I'm using sfp+ interconnects.

 

I found the Dell X4012 BT Business Direct - Dell X4012 Switch L2+ Managed 12 x 10 Gigabit SFP+ (210-AEOQ)

 

Which I can get for less than £600 from the right supplier, can be tandem mounted with a second switch and supports me massively if I want to expand my 10Gb network.

 

I had a webex last night with Dell and they said the switch categorically does not support iSCSI. Obviously this worries me as I don't want to spend around 2k to discover it's not going to work.

 

However I have misgivings over the information Dell gave...

 

1) I don't understand how it can not support it given that it is essentially *just ethernet* unless Dell have chosen to somehow actively block it?

 

2) With the same breath they tried to sell me a SAN fabric with an extra 0 on the end of the price for a 'special 12 hour limited time offer.'

 

So, my question...

 

Anyone using an x4012 in a production iSCSI environment (I've found at least 6 people on forums who say they are)?

Anyone want to lend me one to try?

Can anyone see why they wouldn't work?

 

Help!

[Sagima]

I don't know that much about iSCSI I'm afraid but thanks for pointing me at the switch - it looks like just what I need for my new(er) server room! Most of my knowledge comes from revising to pass the MCSE exams.

 

I didn't think switches needed to do much to work with iSCSI - mostly optimisations rather than allowing/disallowing it. I'm sure it should work on a dumb switch as I believe as everything is worked out by the servers at either end.

 

Dell do have a thing on many of their switches so they work with iSCSI out-of-the-box - if that doesn;t that may be where they got confused (or some certification it hasn't been put through)

[PotNoodleTech]

I can't see why it wouldn't work (that's no guarantee it will work though!)

 

I am pretty sure that back in the old days I experimented with separating Iscsi traffic from the main network just with a cheapo 1GB HP 8 port mini switch and it worked fine.

[sted]

ive had iscsi running on some awful switches in the past (and infact still am in 1 school iirc) granted its just used as an easy way of connecting a backup drive for windows server backup but its works on even unmanaged switches iirc ive had a test setup at home where its being connected to a crummy 5 port asus gb switch and woks fine that's definitely unmanaged so I cant see a managed switch causing you issues unless they have gone out of their way to do so. I suspect the person trying to sell it was reading from a spec sheet and didn't see iscsi so said no

[3s-gtech]

I have iSCSI running between my core and a Cisco SG300 - a budget switch. No issues there. I couldn't guarantee it'll work for certain, but I see absolutely no reason why it wouldn't!

[Oaktech]

Thanks for your responses everyone. You are backing up my theory that Dell were essentially lying to me in the hope of getting more money out!

 

I'm going to order the switches and I'll only un pack them one at a time, try it, and if it works sort the rest of it.

 

I was proper confused because I've had iSCSI essentially running down a wet bit of string before as @sted has, to provide a backup target, so I really couldn't see why it wouldn't work. As @Sagima says there is a Dell iSCSI auto config function on some switches that these don't say that they have, but I can't see why it wouldn't work if I set it up appropriately.

[twin--turbo]

ISCSI is just a TCP/IP based protocol.

 

More ore less any ethernet switch will support it.

 

 

 

TT

[njc235]

I don't know that switch but would suggest packet buffer size might be the issue.

[mrbios]

When i needed something for a similar purchase i spent a while pondering over the expensive option (Cisco SG500XG-8F8T) and a cheap solution which was a netgear thing...they essentially looked the same, but like njc235 points out, packet buffer size, which is quite significant for iSCSI. Ensure that the switch has a large enough packet buffer size to cope with the load you're going to put on it. From the looks of that dell switch, Dell Networking X-Series Smart Managed 1GbE and 10GbE Switches | Dell UK it only has a 1mb packet buffer, so dell would be right in recommending you stayed away from that for the purpose of iSCSI. It will work techincally, but it could cause problems.

 

Same situation i had when i looked into them last year really, I ended up biting the bullet and going with 2 x stacked Cisco SG500XG switches. Not regretting it, expensive, but as a purchase that i hope to last a long long time, not a bad buy.

[Oaktech]

When i needed something for a similar purchase i spent a while pondering over the expensive option (Cisco SG500XG-8F8T) and a cheap solution which was a netgear thing...they essentially looked the same, but like njc235 points out, packet buffer size, which is quite significant for iSCSI. Ensure that the switch has a large enough packet buffer size to cope with the load you're going to put on it. From the looks of that dell switch, Dell Networking X-Series Smart Managed 1GbE and 10GbE Switches | Dell UK it only has a 1mb packet buffer, so dell would be right in recommending you stayed away from that for the purpose of iSCSI. It will work techincally, but it could cause problems.

 

Same situation i had when i looked into them last year really, I ended up biting the bullet and going with 2 x stacked Cisco SG500XG switches. Not regretting it, expensive, but as a purchase that i hope to last a long long time, not a bad buy.

 

Ok, I totally cannot afford to spend 2.5k per switch plus accessories...

 

What about this... D-Link - 8-port 10GBASE-T Smart Switch with 2-port 10G SFP+ and 2-port 10GBASE-T/SFP+ combo ports It doesn't give me any room for additions, but they are less than a grand a switch and have a 2mb packet buffer?

 

Source: http://ftp.dlink.ru/pub/Switch/DXS-1210-12TC/Description/DXS-1210%20Series_A1_User%20Manual_v1.01.pdf

[mrbios]

Ok, I totally cannot afford to spend 2.5k per switch plus accessories...

 

What about this... D-Link - 8-port 10GBASE-T Smart Switch with 2-port 10G SFP+ and 2-port 10GBASE-T/SFP+ combo ports It doesn't give me any room for additions, but they are less than a grand a switch and have a 2mb packet buffer?

 

Source: http://ftp.dlink.ru/pub/Switch/DXS-1210-12TC/Description/DXS-1210%20Series_A1_User%20Manual_v1.01.pdf

 

I'd recommend reading through this post:

which probably explains things a lot better than i can. (Unfortunately the table at the top listing buffer sizes is really old but here it is anyway, and no 10gb options, just in case you can't access reddit: http://people.ucsc.edu/~warner/buffer.html)

 

Those switches weren't £2.5k when i purchased them, I found a supplier doing them for £1.7k each....but that's not really much help here i guess I must admit, when i looked last year there were really limited options in terms of a good 10GB iSCSI switch, there were either the dirt cheap options like the dell and netgear which looked fine for general switching but not up to scratch as dedicated iSCSI switches, or really expensive things over £1.5k each....I hope you find something though, it's been a year since i was looking around so maybe something new on the market.

Edited April 20, 2016 by mrbios

[Oaktech]

I'd recommend reading through this post:

which probably explains things a lot better than i can. (Unfortunately the table at the top listing buffer sizes is really old but here it is anyway, and no 10gb options, just in case you can't access reddit: packet buffers)

 

Those switches weren't £2.5k when i purchased them, I found a supplier doing them for £1.7k each....but that's not really much help here i guess I must admit, when i looked last year there were really limited options in terms of a good 10GB iSCSI switch, there were either the dirt cheap options like the dell and netgear which looked fine for general switching but not up to scratch as dedicated iSCSI switches, or really expensive things over £1.5k each....I hope you find something though, it's been a year since i was looking around so maybe something new on the market.

 

Unfortunately I think I'm going to have to go for the Dell option because I simply cannot afford to do anything else. It's only 2 servers and one enclosure and the traffic is currently not high. I'll look into more accomplished options in my next budget.

[njc235]

Have a look at HPs 2920 with 10g modules. Excellent as iscsi switch with big packet buffers.

[Oaktech]

Have a look at HPs 2920 with 10g modules. Excellent as iscsi switch with big packet buffers.

 

Thanks for this tip...

 

I'm going to get them as one of my suppliers has got a storming deal with HP to get me them for only £500 more than the Dell option.

 

For anyone who is interested, this is what I'm getting:

 

2x HP 2920-24G Switch J9726A

4x HP 2920 2-port 10GbE SFP+ Module J9731A

4x HP X242 SFP+ SFP+ 1m Direct Attach Cable J9281B

 

The DA cables are going between the QLogic (Broadcom) card in the servers and the switch, and the generic SFP+ and OM3 cables I already have are going between the switch and the enclosure. The Lenovo genuine SFP+ are staying in the enclosure.

[sted]

Have a look at HPs 2920 with 10g modules. Excellent as iscsi switch with big packet buffers.

got a stack of them in one of my schools though im not using iscsi both servers are using internal storage the only iscsi is to the backup box and as long as it completes overnight ive not looked into the speed of it (and its got a fibre link to another building with another 2920)