Question about RAID

[dspead]

I ordered a server that's supposed to have RAID 5.

I was curious:

How can I tell if its **REALLY** RAID LEVEL 5?

My research on the net tells me that RAID 5 needs a minimum 3 disk drives -- is this true?

Also -- if one of the drives fails, how will I know?

I assume there are commands I can try that would yield some or all of this information...

Any help is greatly appreciated.
Thanks

[ndelo]

What kind of server did you order? I'm assuming you will run Linux on it. I've been working with compaqs (ML370s) for a year now. They all have hot swap bays. The compaq server setup creates a small partiton that has software utilities to manage the RAID set. Unfortunately, RH 7 will not let me boot to this partition. I guess LILO and it will not play well. However, my RAID card has a ROM chip that also has RAID utilities that let me configure and monitor the card, so to hell with the compaq partition. I'm sure whateve you are using will have something similar. With hardware RAID, the OS has no idea that it is sitting on three, four or more disks. It just thinks you have one huge drive. Winduhs will create an event in the event viewer if something goes wrong with my stripe set (the compaq monitoring agents do this for me). But in Linux, well I don't know. A drive has not failed yet, knock on wood. The RAID card initializers the drives during POST, so I'm sure I'll get a POST error. (I guess this is something I should be sure about). As for knowing that it is indeed RAID 5. You'll know, because you'll most likely have to configure the card or else you won't be able to install your OS. There will be a choice for RAID 5 (stripe set with parity) or something very close to that. It should be fairly straight forward. And if it isn't, there's always product documentation (aka the instructions). RAID 5 has to have a minimum of three disks to work correctly (or at all) so if you bought less, just mirror them.
:)

[ 18 March 2001: Message edited by: ndelo ]

[dspead]

Its a dell 2400 poweredge that came with redhat 6.2 installed.

One reason I questioned thing was that the invoice was for only 2 disk drives.

With all due respect to dell, I'd rather investigate the raid thing myself instead of taking their word that its there, but I don't have the foggiest clue where to begin.

How will I know if one of the drives fail?

Thanks for taking the time to reply.

[ndelo]

If you think it is ok, I would just open the box and peek inside when no one's on. Then you'll know exactly hom many disks are in it. Or poke around the BIOS and see what that says. If there's only two disks on one controller, then your using RAID 1 (mirroring). I would also reboot the machine and see if you there are any messages like so-and-so RAID card initializing array or spinning disks (1 logical drive found) press something or other to enter setup. Also, do you know if it's hardware or software array?
Do you have a RAID card? If so look on the invoice to see what model number, vendor, etc. and browse their website for any documentation you can find. In my limited experience with RAID controllers, they check out the state of the drives before the OS even boots. I've seen one drive fail on a RAID 1 array a while back, and the POST message simply said, "spinning drive...failed, no drive detected." Not to mention that each device in the SCSI chain will get an ID. Just see what's at each ID, tape, hard drive, etc. When something's missing you'll know, I'm sure your machine will not be quiet about it.

[ 18 March 2001: Message edited by: ndelo ]