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iSCSI and packet buffer

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  • 1.  iSCSI and packet buffer

    Posted Jun 13, 2022 01:35 AM
    Hi, we're about to replace our SAN, probably with Dell PowerStore. In the end we'll need two switches for iSCSI, each with 2 x 25 GbE and 4 x 10 GbE. 

    As Aruba is our standard switch supplier, I wanted to use Aruba CX 6300 for that purpose. Now, Dell insists that the switch must have 32 MB packet buffer (or 9 MB if using 10 GbE only) - "to avoid packet loss large buffer is needed. If even just one packet is lost everything need to be retransmitted and that really kills performance."

    Aruba CX 6300 has only 8 MB packet buffer though. Seems like the only Aruba switches with 32 MB are the ones with 48 100-GbE ports.

    How do you see this? Do you think Dell made up the 9 MB requirement to sell their own switches? Or are Aruba switches simply not designed for iSCSI? 

  • 2.  RE: iSCSI and packet buffer

    Posted Jun 13, 2022 05:34 AM
    Hi Stephan, not an expert about iSCSI (I work with FC SAN Fabrics) but it seems that, in your scenario, all boils down to what ports' speeds you have to connect with.

    If I read this DELL Knowledge Base Article correctly, if you're going to connect a iSCSI enabled DELL PowerStore with a 10Gbps network infrastructure then at least a 9MB of Shared Packet Buffer is required (which, as far as I understand, it means that 9MB would be enough), higher speeds require generally deeper packet buffers (thus larger size): 25Gbps seems to require at least 32MB of Shared Packet Buffer.

    At this point the real question would be: is really the Aruba 6300 Switch series suitable for the Ethernet based Storage Network I want to setup considering the specific iSCSI implementation I've in mind?

    To stay on the safe side (and thinking you're going to connect a lot of servers at the speed of 25Gbps) I would say I'm going to use Aruba CX 83xx Switch series (like the 8320, 8325 or 8360 <- all of them provide (a) 32MB Packet Buffer and (b) 10/25Gbps speeds on most port with 40/100Gbps speeds on few ports generally used for uplinks or VSX ISL) but those switches families require a totally different budget compared to the Aruba 6300.

  • 3.  RE: iSCSI and packet buffer

    Posted Jun 13, 2022 05:45 AM
    Thanks! Y, then it seems that CX 6000 series is out of the question. And even CX 8320 has only 16 MB packet buffer if I read the datasheet correctly.

    Looks like we need to get a Dell switch then. Btw, I too don't like iSCSI, it's just so that the existing hosts have iSCSI cards for legacy reasons and we don't want to touch them.

  • 4.  RE: iSCSI and packet buffer

    Posted Jun 13, 2022 06:03 AM
    Sorry, the Aruba 8320 owns "only" 16MB of Buffer Memory for the internal packet processor (so it's less deeper than 8325 and 8360v1/8360v2). In any case those ones are all DC Switches, the same can't be told about Aruba 6300 (which is more devoted to Campus/Access sides).

    Back to your line of reasoning: it's a matter of "price budget" but, keep in mind, it's also a matter of having the right switches for the right duty...I don't know what DELL switch series you're referring to for a like-for-like comparison (considering price/performance) but, in the end, it's up to you ensure your specific network deployment - generally speaking - fits the bill fulfilling all your requirements (not excluded the budget one).

  • 5.  RE: iSCSI and packet buffer

    Posted Jun 13, 2022 06:47 AM
    Hello Stephan,

    You may check Aruba 64xx series switches:

    R0X38A-R0X43A and R0X38B-R0X40B Line Cards: 8MB packet buffer memory per line card
    R0X44A-R0X45A Line Cards: 32MB packet buffer memory per line card


    Hope this helps!


  • 6.  RE: iSCSI and packet buffer

    Posted Jun 13, 2022 07:00 AM
    Y, saw that, but is in different price range too (as only line cards R0X44A and R0X45A have 32 MB, others have only 8 MB like 6300.) Both variants with 32 MB packet buffer (6400 with appropriate line cards or 8325) seem to be somewhere between 60K and 80K € per switch. Dell S5212F-ON (12 x 25 GbE, 3 x 100GbE, 32 MB packet buffer) is between 10K and 20K.

  • 7.  RE: iSCSI and packet buffer

    Posted Jun 13, 2022 07:21 AM
    Well, we have Dell storage and Dell servers, and Dell's switch requirements clearly say that switches must have 32 MB packet buffer. Any Aruba switch for less than 80€K does not seem to meet that requirement, thus would leave our environment 'unsupported' from Dell side (even if it might work). Whereas with the Dell switch it will be supported, and Dell will have to fix it if it doesn't work.

    Easy decision then.

  • 8.  RE: iSCSI and packet buffer

    Posted Jun 13, 2022 10:25 AM
    Well, to be honest - if we look at the number of offered/required ports - the Aruba 8360 16Y2C model (bundled with: Power Supplies and Fans Kit) seems to fit perfectly: it offers 16 ports 1/10/25 GbE (SFP/SFP+/SFP28) + 2 ports 40/100 GbE (QSFP+/QSFP28) and I doubt it will cost you more than 10/12 kEuro (VAT excluded) so quite far from the 80 kEuro you wrote about the Aruba 8325, at least I've seen that price range few times now (about 10kEuro VAT excluded) and the examined offers included also two SFP28 Transceivers, one Universal Rack Mounting kit, the Air Duct kit, a SFP28 DAC cable and also the 3Y Foundation Care support. Just to say. I'm referring specifically to the Aruba 8360 16Y2C v1 bundle (SKUs: JL702A/JL703A) but, I believe, the Aruba 8360 16Y2C v2 bundle (SKUs: JL702C/JL703C) would be near that price zone.

  • 9.  RE: iSCSI and packet buffer

    Posted Jun 13, 2022 10:41 AM
    Hey, indeed that looks the cheapest Aruba solution. 8325 price was so off (for our purposes) that I didn't even check 8360. Still, I couldn't find JL703A cheaper than 20K on quick googling, but will ask quote from our favorite vendor.

    Dell switch is 7K though. 

  • 10.  RE: iSCSI and packet buffer

    Posted Jun 13, 2022 10:58 AM
    The DELL one looks - pardon - "half of a switch" (at least speaking in terms of number of front ports) more or less like the HPE M-series SN2100M or the HPE M-series SN2010M switch series (If I recall they have 16MB Packet Buffer but very low latency)...oh...not an easy decision IMHO.

    QuickSpecs here and here.