CPU for homebuilt SAN

[ihyagp]

I'm throwing together a cheapo SAN machine to throw in my closet any network boot my desktops to cut down on the noise in my geek lair. What's the minimum CPU I'd need to reliably saturate gigabit with iscsi? How about duplex gigabit?

 

[yinan]

How are you going to network boot everything? Do you not know that is easier said than done? But to answer your question, and low wend dual core will work. To saturate the link you will need more disk I/O than network.

 

[ihyagp]

Probably pxe->gpxe chain with dhcp and tftp running on the san. If I can find a ataoe driver that works with win7 x64 I'll go that route, otherwise iscsi.

Think any of the new atoms would do it? Or via nano?

edit: i'd love to go fanless with this too.. but its not critical. and disk io isn't an issue, the slowest drive will be a 1.5tb 7200.11 (inb4 spontaneous bricking, i know i know)

 

[yinan]

You do realize that you will need hardware iSCSI to do this as well. Disk IO will be a problem when streaming an OS.

 

[ihyagp]

I'd done it with out-of-the-box tgtd (no hardware assist) and got 90 megs/second over gigE. No special hardware needed. That was with a c2d e6600 though - that's why I'm asking about CPU.

 

[imagoon]

disk io isn't an issue, the slowest drive will be a 1.5tb 7200.11

Heh, I wouldn't agree with you. Maybe if your only running 1 machine of your SAN that 1 disk is fine...

Otherwise 1 disk is not enough disk IO unless you really don't care that your disk subsystem's performance is only 25 to 75% of what it was. Sequential disk means almost nothing with your plan to network boot desktops (since you used plural) there. TCP/IP overhead combined with disk seek latency is where it is at.

If you plan to put Internet on this same Ethernet port your in for a rude awakening.

I would expect... Either A) a rather current cpu, as a one of the Core processors or TCP/IP offload cards and a weaker processor with 2-5 disks of the same speed and type to get your disk arm count up.

 

[ihyagp]

Heh, I wouldn't agree with you. Maybe if your only running 1 machine of your SAN that 1 disk is fine...

Otherwise 1 disk is not enough disk IO unless you really don't care that your disk subsystem's performance is only 25 to 75% of what it was. Sequential disk means almost nothing with you plan to network boot desktops (since you used plural) there. TCP/IP overhead combined with disk seek latency is where it is at.

It'll be one machine per disk in the SAN (going to just migrate the existing machines' drives over to the san). I'm hoping to avoid layer 3/4 overhead by using ATAoE, but we'll see.

If you plan to put Internet on this same Ethernet port your in for a rude awakening.

Really? My internet is only 12 megabits and the network is all-gigabit. Is it just a bandwidth issue or is something else in play as to why I shouldn't have SAN and internet on the same NIC?

I would expect... Either A) a rather current cpu, as a one of the Core processors

Maybe an i3 underclocked enough to run fanless?

 

[ihyagp]

Ancillary question to this: Does anyone know of a router that will let me run jumbo frames on my LAN and re-encapsulate them at layer 3/4 so anything going out to the internet has a 1500MTU?

 

[imagoon]

It'll be one machine per disk in the SAN (going to just migrate the existing machines' drives over to the san). I'm hoping to avoid layer 3/4 overhead by using ATAoE, but we'll see.



Really? My internet is only 12 megabits and the network is all-gigabit. Is it just a bandwidth issue or is something else in play as to why I shouldn't have SAN and internet on the same NIC?


Maybe an i3 underclocked enough to run fanless?

To answer this and your second post...

iSCSI and anything like "ATAoe" is going to be heavily disturbed by unrelated traffic on the lines. You typically run Jumbo frames to reduce the CPU load on the network, not for better through put. You also use flow control and a decent switch that supports it. Both are detrimental to 'Internet.'

 

[imagoon]

Ancillary question to this: Does anyone know of a router that will let me run jumbo frames on my LAN and re-encapsulate them at layer 3/4 so anything going out to the internet has a 1500MTU?

I am sure cisco and the like can do it. However it would be cheaper to just buy a small jumbo frame/flow control supporting switch and leaving all disk traffic on its own LAN.

 

[pitz]

What software are you running on the SAN host?

And I disagree with the other posters -- there shouldn't be performance problems with this setup. Its pretty rare to have HDDs in even desktop PC's do sequential bursts >50mb/sec, nevermind 100+mb/sec that is possible with Gig-E.

As for what you'll need CPU-wise, basically anything that fits on a PCI-E motherboard will do just fine (because you'll obviously need the PCI-E bandwidth for your disks) if your solution is reasonably optimized. Even an old AthlonXP 2500+ can saturate Gig-E in a basic streaming application using Samba, and iSCSI is certainly less CPU intensive than Samba/SMB.

BTW, I'd love to know how you're gonna get WinXP/WinVista/Win7 to boot with gPXE/etc., without an iSCSI boot ROM. Could you write a HOWTO or something? I desperately want to get rid of hard drives here and would love to use a similar sort of solution instead of clunky and unmanaged/unRAID'ed disks.

 

[ihyagp]

OK, thanks. I'll see how it looks with everything on one line. It wouldn't be a problem to set up a 2nd network in parallel just for disk access, but it is only 3 machines, none of which deal with much data.

 

[ihyagp]

What software are you running on the SAN host?
BTW, I'd love to know how you're gonna get WinXP/WinVista/Win7 to boot with gPXE/etc., without an iSCSI boot ROM. Could you write a HOWTO or something? I desperately want to get rid of hard drives here and would love to use a similar sort of solution instead of clunky and unmanaged/unRAID'ed disks.

http://www.etherboot.org/wiki/pxechaining

This is pretty close to what I followed. I didn't use a script served up by DHCP though, just a single gpxe image with a script embedded.

edit: ok reading this further, its not all that close. i used a dhcp server that next-server pointing to a machine running a tftp server, and "filename" set to an image generated here, with the sanboot command embedded - http://rom-o-matic.net/gpxe/gpxe-1.0.0/contrib/rom-o-matic/

Just plain linux tgtd as the iscsi target. - http://fedoraproject.org/wiki/Scsi-target-utils_Quickstart_Guide is what I followed, except I'm using an actual partition rather than a loopback to a file.

 

[Emulex]

check out the new hp thin clients - they don't use pxe boot but they are thick clients - the server delivers the o/s over lan using something (new?).

ATAOE works really with decent switches hp procurve or nicer. iscsi is actually far far far more forgiving with using cheap switches (or no switches!).

 

[ihyagp]

check out the new hp thin clients - they don't use pxe boot but they are thick clients - the server delivers the o/s over lan using something (new?).

Will probably go thin client for the living room once I learn more. This just for my geek cave though, which includes a gaming machine, so I don't want to replace them.

ATAOE works really with decent switches hp procurve or nicer. iscsi is actually far far far more forgiving with using cheap switches (or no switches!).

Thanks. Good to know. I don't really have the budget for high-end switches (would just get ssd's otherwise) so iscsi it is then. Just out of curiousity - do you know of any ataoe drivers that work with win7 x64?