Introduction

For years, centralized storage meant complex Fiber Channel Storage Area Networks (FC SAN) which were very expensive. Large enterprises were prepared to pay big premiums for such centralized storage networks, as storing valuable data scattered over hundreds of servers would cost them a lot more. The risk of losing data was higher, and decentralized storage resulted in a lot more work for the system administrators. As the necessary storage capacity doubled and still doubles every 18 months, scalability not simplicity was the priority. Hence, the expensive but scalable SANs paid for themselves over time by making the datacenter easier to maintain with fewer people and lower data loss risks.

However, for an SME (Small/Medium sized Enterprise), SANs were simply overpriced storage arrays. The SME has fewer servers that need access to shared storage, so complex switching fabrics with routing are usually unnecessary. The need for less storage capacity and more simplicity doesn't mean that centralized storage capacity cannot be a huge advantage for some SMEs. SMEs that offer web services are especially interested in an affordable form of centralized storage.

We have been working with quite a few SMEs the past several years, and making storage more scalable is a bonus for those companies. However, it is not the main reason companies are looking into SANs. If your company depends on a web service, you want your server to be available around the clock. That means that you will almost certainly be looking towards clustering and failover techniques. These High Availability (HA) technologies - whether on a virtual (VMware HA, Xen HA) or a physical server - in many cases require a shared storage device to work well.

HA together with making storage easier to maintain are the two main reasons why affordable shared storage is desirable, even in an environment where only a few servers are necessary. VMware's Vmotion is another reason why the interest for centralized storage is increasing. Vmotion is not really an alternative for the traditional failover and HA technologies, but it allows for hardware maintenance and server migration from one machine to another without any downtime. In order to make this work, you also need shared storage.

The SME's renewed interest for centralized storage has drawn the attention of the big storage vendors. Since 2006, HP, Netapp, Sun, IBM, Fujitsu-Siemens, and EMC have all launched quite a few product lines targeted at the SME. Many of these "SME products" start at a relatively low price, but a complete storage solution can still carry a very hefty price tag. It is not surprising that the SME product lines are in fact somewhat downsized high-end solutions if you consider that the SME market (about $1 billion) is probably only a small fraction of the $17 billion storage market (See IDC's 2006 report).

Anyway, the idea behind this article is not to discuss the technology and business trends in the professional IT market. There are enough articles covering that. As part of a larger project of helping the SMEs with their datacenter choices, we will try to find out which solutions offer good price/performance without omitting any critical features. If you are relatively new to storage, we'll give you a crash course.
Storage Crash Course...
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  • Anton Kolomyeytsev - Friday, November 16, 2007 - link

    Guys I really appreciate you throwing away StarWind! W/o even letting people know what configuration did you use, did you enable caching, did you use flat image files, did you map whole disk rather then partition, what initiator did you use (StarPort or MS iSCSI), did you apply recommended TCP stack settings etc. Probably it's our problem as we've managed to release the stuff people cannot properly configure but why did not you contact us telling you have issues so we could help you to sort them out?

    With the WinTarget R.I.P. (and MS selling it's successor thru the OEMs only), StarWind thrown away and SANmelody and IPStor not even mentioned (and they are key players!) I think your review is pretty useless... Most of the people are looking for software solutions when you're talking about "affordable SAN". Do you plan to have second round?

    Thanks once again and keep doing great job! :)

    Anton Kolomyeytsev

    CEO, Rocket Division Software
    Reply
  • Johnniewalker - Sunday, November 11, 2007 - link

    If you get a chance, it would be great to see what kind of performance you get out of an iscsi hba, like the one from qlogic.

    When it gets down to it, the DAS numbers are great for a baseline, but what if you have 4+ servers running those io tests? That's what shared storage is for anyhow. Then compare the aggregate io vs DAS numbers?

    For example, can 4 servers can hit 25MB/s each in the SQLio random read 8kb test for a total of 100MB/s ? How much is cpu utilization reduced with one or more iscsi hba in each server vs the software drivers? Where/how does the number of spindles move these numbers? At what point does the number of disk overwhelm one iscsi hba, two iscsi hba's, one FC hba, two FC hbas, and one or two scsi controllers?

    IMHO iscsi is the future. Most switches are cheap enough that you can easily build a seperate dedicated iscsi network. You'd be doing that if you went with fiber channel anyhow, but at a much higher expense (and additional learning curve) if you don't already have it, right?

    Then all we need is someone who has some really nice gui to manage the system - a nice purdy web interface that runs on a virtual machine somewhere, that shows with one glance the health, performance, and utilization of your system(s).

    System(s) have Zero faults.
    Volume(s) are at 30.0 Terabytes out of 40.00 (75%)
    CPU utilization is averaging 32% over the last 15 minutes.
    Memory utilization is averaging 85% over the last 15 minutes.
    IOs peaked at 10,000 (50%) and average 5000 (25%) over the last 15 minutes.

    Pinch me!

    -johhniewalker
    Reply
  • afan - Friday, November 09, 2007 - link

    You can get one of the recently-released 10Gbps PCI-E TCP/IP card for <$800, and they support iSCSI.

    here's one example:
    http://www.intel.com/network/connectivity/products...">http://www.intel.com/network/connectivi...oducts/p...
    The chip might be used by Myricom and others, (I'm not sure), and there's a linux and a bsd driver - a nice selling point.

    10gb ethernet is what should really change things.
    They look amazing on paper -- I'd love to see them tested:
    http://www.intel.com/network/connectivity/products...">http://www.intel.com/network/connectivi...ucts/ser...
    Reply
  • JohanAnandtech - Saturday, November 10, 2007 - link

    The problem is that currently you only got two choices: expensive CX4 copper which is short range (<15 m) and not very flexible (it is a like infiniband cables) or Optic fiber cabling. Both HBAs and cables are rather expensive and require rather expensive switches (still less than FC, but still). So you the price gap with FC is a lot smaller. Of course you have a bit more bandwidth (but I fear you won't get much more than 5 GBit, has to be test of course), and you do not need to learn fc.

    Personally I would like to wait for 10 gbit over UTP-cat 6... But I am open to suggestion why the current 10 gbit would be very interesting too.
    Reply
  • afan - Saturday, November 10, 2007 - link

    Thanks for your answer, J.

    first, as far as I know, CX4 cables aren't as cheap as cat_x, but they aren't all _that_ expensive to be a showstopper. If you need more length, you can go for the fibre cables -- which go _really_ far:
    http://www.google.com/products?q=cx4+cable&btn...">http://www.google.com/products?q=cx4+ca...amp;btnG...

    I think the cx4 card (~$800)is pretty damn cheap for what you get: (and remember it doesn't have pci-x limitations).
    Check out the intel marketing buzz on iSCSI and the junk they're doing to speed up TCP/IP, too. It's good reading, and I'd love to see the hype tested in the real world.

    I agree with you that UTP-cat 6 would be much better, more standardized, much cheaper, better range, etc. I know that, but if this is we've got now, so be-it, and I think it's pretty killer, but I haven't tested it : ).

    Dell, cisco, hp, and others have CX4 adapters for their managed switches - they aren't very expensive and go right to the backplane of the switch.

    here are some dell switches that support CX-4, at least:
    http://www.dell.com/content/products/compare.aspx/...">http://www.dell.com/content/products/co...er3?c=us...

    these are the current 10gbe intel flavors:
    copper: Intel® PRO/10GbE CX4 Server Adapter
    fibre:
    Intel® PRO/10GbE SR Server Adapter
    Intel® PRO/10GbE LR Server Adapter
    Intel® 10 Gigabit XF SR Server Adapters

    a pita is the limited number of x8 PCI-E slots in most server mobos.
    keep up your great reporting.
    best, nw
    Reply
  • somedude1234 - Wednesday, November 07, 2007 - link

    First off, great article. I'm looking forward to the rest of this series.

    From everything I've read coming out of MS, the StorPort driver should provide better performance. Any reason why you chose to go with SCSIPort? Emulex offers drivers for both on their website.
    Reply
  • JohanAnandtech - Thursday, November 08, 2007 - link

    Thanks. It is something that Tijl and myself will look into, and report back in the next article. Reply
  • Czar - Wednesday, November 07, 2007 - link

    Love that anandtech is going into this direction :D

    Realy looking forward to your iscsi article. Only used fiber connected sans, have a ibm ds6800 at work :) Never used iscsi but veeery interested into it, what I have heard so far is that its mostly just very good for development purposes, not for production enviroments. And that you should turn of I think chaps or whatever it its called on the switches, so the icsci san doesnt overflow the network with are you there when it transfers to the iscsi target.
    Reply
  • JohanAnandtech - Thursday, November 08, 2007 - link

    quote:

    Love that anandtech is going into this direction :D


    Just wait a few weeks :-). Anandtech IT will become much more than just one of the many tabs :-)

    quote:

    And that you should turn of I think chaps or whatever it its called on the switches, so the icsci san doesnt overflow the network with are you there when it transfers to the iscsi target.


    We will look into it, but I think it should be enough to place your iSCSI storage on a nonblocking switch on separate VLAN. Or am I missing something?

    Reply
  • Czar - Monday, November 12, 2007 - link

    think I found it
    http://searchstorage.techtarget.com/generic/0,2955...">http://searchstorage.techtarget.com/generic/0,2955...

    "Common Ethernet switch ports tend to introduce latency into iSCSI traffic, and this reduces performance. Experts suggest deploying high-performance Ethernet switches that sport fast, low-latency ports. In addition, you may choose to tweak iSCSI performance further by overriding "auto-negotiation" and manually adjusting speed settings on the NIC and switch. This lets you enable traffic flow control on the NIC and switch, setting Ethernet jumbo frames on the NIC and switch to 9000 bytes or higher -- transferring far more data in each packet while requiring less overhead. Jumbo frames are reported to improve throughput as much as 50%. "

    This is what I was talking about.

    Realy looking forward to the next article :)
    Reply

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