What is IT-mode?

[lippy]

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]

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]

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.

 

[odditory]

^ These guys know what they're talking about.

 

[lippy]

Thanks guys!

 

[neail]

So,
IT mode = JBOD = Non-raid... to allow software raid and disable hardware raid to avoid conflicts between hardware raid and software raid.

I believe JBOD and Raid 0 are not equivalent,

for example- if one solid file (like a video file/ archive....not multiple files in a folder) - is copied into a system
for RAID 0 it will be divided into disks
for JBOD the solid file will remain on one disk, basically, files will be split as a whole in disks.

please correct me if I am wrong.

 

[mobilenvidia]

You can setup RAID0 on 1 disk, only way most modern RAID controllers can have individial drives, as JBOD feature LSI removed way back in the day

If you want all the drives to be seen as they are get an HBA in IT mode

RAID is for setting up arrays of drives usually either for raw speed or hardware redundency or in RAID 10 both

 

[neail]

You can setup RAID0 on 1 disk, only way most modern RAID controllers can have individial drives, as JBOD feature LSI removed way back in the day

If you want all the drives to be seen as they are get an HBA in IT mode

RAID is for setting up arrays of drives usually either for raw speed or hardware redundency or in RAID 10 both

Thank you for your time,
And for single disk raid 0 info.
Having little confusion here,
Are JBOD and It mode different protocols? Or JBOD term is LSI specific?

 

[mobilenvidia]

JBOD is a general term
Don't what ever you do is get a RAID card and run single drive RAID0 drives you will be dissapointed
HBA all the way for any Software RAID NAS

 

[neail]

JBOD is a general term
Don't what ever you do is get a RAID card and run single drive RAID0 drives you will be dissapointed
HBA all the way for any Software RAID NAS

Yes, I am aware of that, to flash the firmware, I do not intent to have any hardware RAID under software one. Thank you again.