Re: Firewire Cards/Drive and Linux RAC

"You like me! You really like me!"

Both firewire and SCSI support more than two nodes - though its only generally practical with Firewire. While the firewire disk is dual ported, there are a couple of tricks you can use to get more than two nodes hooked up to it. One is to buy a firewire hub - that can get you to four nodes. The other way, which is uglier, is that most of the firewire cards on the market that have multiple ports effectively implement a firewire hub within the card. That is to say, all of the ports on a card exist within a single firewire network and a single controller chip. So, what you can do is cable two hosts directly to the disk, and then cable a third host to another port on one of the two already-connected hosts, and it will get access to the disk. Of course, should that intermediary host lose power, both hosts will lose access. I think the max in either scenario is four nodes - we don't scale our firewire clusters any larger than that, because the only reason we get that big is benchmarking, and we use proper servers and storage for that.

SCSI is hard - you need either a SCSI hub or a disk array with many ports, and those are hard to find.

Fibre Channel is designed for this - basically, you need an array and a hub or switch. Used, you're probably looking at $8k-10k for some hbas, old fibre channel storage, and a hub or switch. Fibre is expensive - stick with firewire if you're just playing around.

Also, another option that is not officially supported, but works, is iSCSI. It's a bit of a hassle, but you can get the iSCSI target implementation from http://www.ardistech.com/iscsi/ . You basically create raw devices, and then export them via the driver. Then you can use the downloadable cisco iscsi initiator to access them - they show up as local disks, fairly cool. In order to get any reasonable performance, you're going to need Gigabit ethernet. Again, its a hassle, but you can hook a lot of nodes up this way at a very low incremental cost.

Thanks,
Matt

--
Matthew Zito
GridApp Systems
Email: mzito_at_gridapp.com
Cell: 646-220-3551
Phone: 212-358-8211 x 359
http://www.gridapp.com


On Jun 18, 2004, at 11:18 AM, Peter Miller wrote:



> Cheers Matt,

>

> you are my 10g RAC hero guru. I'll get onto ebay straight away.

>

> Once I've got some experience and success with the firewire set-up, 

> I'll

> have a go at the SCSI cluster. I'm considering at getting a pair of

> Adaptec 39320A-R cards and a Dell PowerVault 221S with cluster/split 

> bus

> module.

>

> One thing that does bug me is that both the firewire and SCSI have dual

> ports that limit them to 2 nodes. Not very scaleable. Ignoring NAS (

> i.e. NetApps), what h/w supports 3+ nodes ? Is it SAN ?

>

> If so any ideas about the price differential between SCSI and SAN. I

> guess I'm looking at £3.5k for the SCSI array and RAID cards. How much

> for a SAN implementation? Any ball park figures appreciated


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