RAID on OSX?

[digiculture]

Ok. This might be a silly question since i know very little about RAID but I'll ask anyway. I've heard that RAID can be used to make two identical hard drives work together as one, thus delivering faster performance. I have also noticed a RAID section in the OSX Disk Utility. What exactly does that do? Is it a software RAID controller that could enable you to plug two identical ATA drives to the hard drive bus (I have an AGP graphics G4 450MHZ) and use them as one? Please tell me it is!

Any help would be very nice.

 

[digiculture]

Oh and by the way, if this is a software RAID controller, how well does it work?

 

[Chisholm]

hhhmmmm.....
RAID on a Mac is kinda' new to me, but I'll offer my experiences...There are different types of RAID. The most common are "mirroring" and "striping." Mirroring takes at least two drives and writes the same data to both drives. In theory, if one drive dies the machine keeps going. In practice on an OSX server X.1.4 (a coworker told me this, but it wasn't exactly a controlled testing environment) the sh*t doesn't work. With striping, the OS takes the given amount of data to be written to the hard drive and splits it between the drives. So, in theory, if you have 2 drives half the time is needed for the operation. My experience with this is with a (no flames for this please!) PeeeCeee I have at home. It is a dual 1GHZ PIII that has 100mbs dual channel RAID built in. I have 2 30 GB drives that are striped. For disk intensive stuff I can tell there is a speed gain. For playing Quake 3 I notice nothing. When restoring a ~1.5GB disk image it takes 3 minutes or less. On a P4 2.53GHZ machine here at work with a 1.5 GB image it takes about 8 minutes to restore. Oh, with striping you get the whole disk size, so my 2 30 gig drives show up as a single 60 gig drive. Problem is, if one drive dies, half your data is gone...i.e. you be screwed!

I plan to test mirroring stuff on my new dual 867 mirror mac here soon. I am wary of software RAID. I think Apple will integrate hardware RAID in the Xserver at some point.

anyway, just my experiences. If I can help let me know.

cheers!
John

 

[TheT]

I don't know much about this either and actually never used it, but as far as I know, you can select any drives you want there and make em work as one, yes.

 

[mischief]

Here's some detail:

It's a Software RAID, meaning that the OS is doing the work of assigning what data goes where. As you can imagine this has some limitations.... not the least of which is: You can't boot from it.... period.

If you want Data integrity backup from Mirroring (RAID Zero) But still want to boot the machine.... you'll need a 3rd drive.

No matter how you slice it to do a RAID effectively you'll want a Host-Card, prefferably one that's both fast AND has built in Hardware RAID. A Sonnet ATA-133 RAID card is exactly that and runs U about $200.00 USD.

If you're going to do it, do it right: Get a good, fast host card and 2 identical ATA-133 drives and do a RAID Zero (Mirror) so your data is close to totally backed up ALL THE TIME.... Then get yourself a smaller drive to be a boot drive and call it good. The fast host-card will gain you all the speed you're likely to get over a 100 or 133 Bus.

 

[evildead]

Raid and proformace

If your looking for Proformance.. dont use RAID. Software RAID has tons of over head and it will slow you down. If you want to miror for disaster recovery.. thats diffrent.

You can get a hardware RAID device.. but that costs alot and not worth it for most home users.

If your worried about proformance and you want to mirror drives... I would just rsync and set it up to sync up late at night when your not using it.