RAID and HD's: EXACTLY the same drives...or close enough? Maxtor says....

[MichaelD]

Sometimes I just don't know how to word my titles; too long, you know? Anyway, here goes.

OK, here is what I know as fact:
I already know that if you use two different size drives in a RAID array, the size of your array will be the size of the smallest drive, times the number of drives in the array. I know that you cannot use a 5400rpm and a 7200rpm drive together in a raid array.

So, I decide to check with the source on something...just to be 100% sure.

I just got off the phone w/a customer service rep at Maxtor. He was nice, but he didn't seem too well versed on RAID. My question to him was this:

"I have two Maxtor DiamondMax Plus, 7200rpm, ATA100 drives. One is a 45gig the other a 40 gig. Can I use them in a RAID array?"

He told me "no you cannot, they have to be the exact same drives with the exact same model number."

Is this correct? If it is, then I have to go buy another 40gig drive in addition to the one I got last night. Well heck, then I'll have an 80gig RAID 0 array and a 45gig backup drive all in the same case. Storage up the wazoo. Please enlighten me on this.

 

[MadRat]

Shouldn't have to be the same. You should be able to run equal partitions in RAID.

 

[Dulanic]

No they dont have to be the same, but you will lose that extra 5 GB. RAID 0 is only as fast as your slowest drive (access time wise). Its read rate can at MAX be 2x your slowest drive.

 

[bigbootydaddy]

yeah, you will lose the 5gb, but, can u mix the 5400 and 7200?

 

[MichaelD]

Thanks guys, that is good news. You know, I lost 2.5 gigs just thru the formatting process! From what I've read (here on AT forums) this is normal. Bummer. Drivespace says I have a 42.5 gig HD. Oh well.

B3 (BigBootyDaddy...or "B Cubed" ),
I don't have two different speeds, just two different capacity drives. They are both ATA100/7200rpm. Just one is 45 the other is 40 gig.

 

[CQuinn]

FWIW, the Maxtor rep gave you the proper "corporate" answer, if not the
best technical answer.

As you pointed out, running dissimilar drives (5400rpm and 7200rpm) are a
bad idea in a RAID setup (the timing between the two drives would be too far
off for accurate data streaming).

By the same logic, running anything but two of the same model drive can introduce
inconsistencies in the RAID array that might cause instability. Most of us
here in the forum would say "go for it" because we know where to draw the line
at acceptable levels of instability; and if something goes wrong, we can't be
blamed for giving free advice

For a company like Maxtor there is no such line, because they'd end up being
financially liable if someones system crapped out because they told them mixing
drives in a RAID is okay.

Sometimes the "right" answers you get from the company are not the same "right"
answers you get in the real world.

 

[MichaelD]

CQuinn,

I was gonna PM you, but it's not turned on. So, are you saying (yes, I know that you're not liable if I blow myself up) that I should be OK with the two drives I'm planning on using?

The are both:
Maxtor DiamondMax Plus
ATA-100
7200RPM
Even have the same seek time specified of 8.7ms

The only difference (as far as the spec sheets go) is the capacity...45 vs 40gigs. Thanks bud.

 

[Noriaki]

Hmmm
your 40Gig is probably 10Gigs/platter, whereas your 45gig is porbably 15....that could make for some inconsistancies in data location.
For example, the 11th Gig, on the 40 gig drive, is the start of the 2nd platter. On the 45gig drive it's 2/3s of the way through the first....

I don't know if that really matters, but personally I wouldn't do it.

A 30Gig DiamondMax+45 and a 45Gig DiamondMax+45 I would do (for a 60gig, 15gig/platter 2 platters per drive setup). But I wouldn't pair up a DM+45 with a DM+40.

Again, my opinion, I'm not a RAID expert.

 

[MichaelD]

Hi Noriaki,

Wow, that is definitely a proper scientific explanation. I know a tiny (real tiny) bit about platter density, but didn't think it would matter. Buzzzz..wrong answer. Obviously, it does. Oh well, gotta go get another drive tonight. I guess I will now have an 80gig RAID 0 array and a 42.5 (after formatting) backup drive. Glad I got the 400w power supply! I'd have been very upset to find that my array didn't work or didn't work correctly. I appreciate the info hookup. Thank you Noriaki.

 

[RedShirt]

Actually... The 40 gig 7200 RPM is 20 gigs per platter and the 45 gig is 15 gigs per platter. The 40 is actually faster than the 45.

Edit: Not that it changes the eplanation at all.