What is IT-mode?

lippy

New Member
Jun 29, 2011
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Yea, a real noob question. But I’d like someone to explain why the IBM M1015 cards are being flashed to that. I don’t understand what IT-mode is (or isn’t).

Background:
I’m building slowly. Norco 4220, Tyan S5512WGM2NR. Going to run WHS v1 with duplication. The decision the pickup 2 M1015 cards off of fleabay were that they were cheaper than AOC-SASLP-MV8 cards. And by using the M1015 card that would future-proof the hardware if I ever wanted to go to WHS2008 and run “duplication†as RAID 1 through the M1015 card.

Can someone explain what IT-mode is or point me to a link so I can read up on it?

Thanks.
 

dswartz

Active Member
Jul 14, 2011
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IT mode stands for "initiator target". It presents each drive individually to the host. IR mode is in whatever raid formats the HBA supports. Some allow you to present drives individually as JBODs or raid0 with one drive each, but if you are going to do that, it makes more sense to flash to IT, since the firmware is smaller and more efficient (supposedly...)
 

Patrick

Administrator
Staff member
Dec 21, 2010
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To add to dswartz's post, one of the biggest reasons for going into IT mode is to remove the RAID firmware from systems that will use software RAID. If you think about it, upon an error, you have three things that could potentially fix the problem:
1. Disk onboard controller
2. RAID controller
3. SW RAID
The problem is, the disk's onboard error checking, the RAID controller, and the software RAID implementation do not all fully know what the others are doing. Putting IT firmware on the controller makes it a "dumb" pass-through device basically eliminating #2 on the list above. Some of the custom firmware that big storage vendors use on drives are an attempt to harmonize #1 and #3 above.