Welcome to the MacNN Forums.

l008com · May 28, 2003, 02:39 AM

Can you boot off of RAID setups made with Disk Utility? I know in 10.1 Apple RAID's were not bootable, but have the 'fixed' this in 10.2?

rhansen_x · May 28, 2003, 08:48 AM

Does the raid unit use a hardware controller or software?

gadster · May 28, 2003, 10:23 AM

Originally posted by l008com:
Can you boot off of RAID setups made with Disk Utility? I know in 10.1 Apple RAID's were not bootable, but have the 'fixed' this in 10.2?

Yeah, I got 2 120mb disks mirrored. Boots with no drama. However, I can't install classic. Or anything that requires a classic installer...

Le DANG. As they say in Paris.

coitus · May 29, 2003, 06:28 PM

Okay, I just bought two 160 GB 7200 RPM Maxtor drives today from CompUSA (only $200 total after rebates) and want to set up my mirrored 2-drive RAID.

Do I need a play by play instruction set or...

1) pop the drives in...

2) make one master and one slave.

3) use disk utility to identify them as a mirrored-array...

4) Install 10.2 and away we go??

thanks,

coitus

l008com · May 29, 2003, 08:08 PM

I'm pretty sure if you do a mirrored IDE Raid with one master and one slave, its going to be really slow, it will cut the performance in half, becuase it has to talk to both drives to read and write, and if they are on the same bus, it can only talk to one at a time. So it would have to slowly switch back and forth.

Brass · May 29, 2003, 09:21 PM

Originally posted by l008com:
I'm pretty sure if you do a mirrored IDE Raid with one master and one slave, its going to be really slow, it will cut the performance in half, becuase it has to talk to both drives to read and write, and if they are on the same bus, it can only talk to one at a time. So it would have to slowly switch back and forth.

you're correct for writing, although if the drives were on seperate controllers, the difference would be negligible and not noticible.

But for reading it should theoretically be more efficient. You only have to read from ONE mirror. A well written RAID mirror, using disks on separate controllers will be able to read different files (or even blocks of files) from both drives at the same time, making things somewhat faster for reading.

Actually, I just realised, you're talking IDE, which I'm not familiar with. I'm thinking of SCSI disks.

coitus · May 29, 2003, 10:07 PM

After a little bit of research...I realized I left out one very important fact. My computer a G4 450 DP running 10.2.6 won't support any more than 128 GB.

As a result, I am looking at purchasing the ACard Ultra-ATA Hardware RAID 0 from http://www.macsales.com/. It runs for about $160...I am guess that a hardware RAID option will be better than software anyway.

The card states the following:

RAID Function:
Supports true Hardware RAID 0 (Striping), RAID 1 (Mirroring). Capable Booting from standard and RAID volume.

Features:
True Mac OS X support.
A standalone PCI-to-IDE RAID controller.
At a normal mode as IDE devices extension. OS X, OS 8.5, OS 9 all on same firmware.
Supports capacity larger than 137GB Hard disk.

Specifications:
DIP Switch setting for RAID 0 mode, RAID 1 mode or normal mode. Coexist with on-board. IDE controller. Open Firmware interface. Max. 4 IDE devices

PCI Bus:
32-bit PCI Bus Master for up to 133MB/s data transferring rate. Scatter / Gather function support. Automatic FIFO threshold selection. Low command overhead. True PCI Plug and Play

IDE Bus:
Dual independent channel of IDE bus. Supports Ultra ATA133/100/66/33 hard disk.
Supports 48-bit addressing with Big Drive technology. Data transfer rate up to 133MB/sec per channel.

OS Compatibility:
Mac OS X, Mac OS 8.5, OS 9 and higher.

As for why this card...a buddy of mine has just the normal PCI ACard and reports it works great. I still want to ensure I can boot from one of the mirrored drives, but I'm guessing that is what the "capable booting" stuff is all about.

I'm completely new to this so I do appreciate any helpful advice or suggestions.

coitus

Tyre MacAdmin · May 29, 2003, 10:28 PM

Originally posted by gadster:
Yeah, I got 2 120mb disks mirrored. Boots with no drama. However, I can't install classic. Or anything that requires a classic installer...

Le DANG. As they say in Paris.

lol you're Le Killing me...

silverghost · May 29, 2003, 10:53 PM

hi all, im also thinking of setting up a raid for backup and a fast scratch disc. will it work if my steup is firewire?

sorry i couldnt contribute to the original post.

ill be using it with a TiSD. ive already got the enclosure, and one 120gig hd. ill be getting another hd later this week.

aloha

Spliffdaddy · 01:37 AM

here is some general info that might help...

'Software' RAID 0 striping usually requires support from the operating system. For this reason, 'software' striped arrays cannot be made bootable.

A single IDE (ATA) channel can support 2 devices (disks, optical drives) - but can only communicate with one device at a time (just like SCSI). Most desktop computers have 2 IDE channels with support for 2 devices on each of those channels. For 'software' RAID striped arrays you want the disks to reside on separate channels (placing them on the same channel yields no benefit since only one of the disks can be addressed at any given moment). This means you are limited to 2 disks for a 'software' striped array (if you have 2 channels of IDE). Well, you can stripe across more than 2 disks (3 or 4), but there will be no benefit unless you have a channel for each disk. The same is true with SCSI controllers. Most have 2 channels, just like IDE. SCSI can support more devices per channel (7 typically) than IDE, but still can only address ONE at a time. A couple of years ago, just for kicks, I 'software' striped a set of seven 4.3GB Seagate Barracuda SCSI drives using Win2000. Sure enough, my 2 channel SCSI card throttled any performance gain after the 2nd drive was added. Hell, I could have used 14 Barracudas in my array - but there was nothing to be gained.

Firewire-connected and other 'removeable' disks are usually not allowed to be part of a 'software' RAID array...the reason being, I assume, is because they stand a good chance of being mixed-up or might be missing necessary disks in the array. While it's possible to use removeable disks as part of a software RAID - the operating system generally won't allow it. I don't think it's possible with OSX nor Windows.

You can use a non-RAID (regular) IDE (ATA) PCI expansion card to support disks larger than your onboard IDE controller is capable of supporting. This will allow you use 'software' RAID striping instead of having to buy a pricey RAID card. You're limited to striping (RAID 0) only with 'software'. If you want data redundancy (the ability to rebuild failed drives) or if you wish to boot from a striped array, you'll need a hardware solution, aka IDE RAID card. You can boot your OS from a hardware-based striped array. Something you can't do using software RAID. The RAID card presents the array to the OS as a single disk. It lies, lol. The operating system thinks it's a single disk and treats it as one. The RAID card's controller hardware handles the read/write operations and maintains the array.

'Software' based RAID has proven itself to be quite reliable, in MY experience. There is no measureable difference in performance between hardware and software striped arrays. Seriously. There is very little CPU loading for 'software' RAID.

RAID 0 "striping" can double(!) both read and write disk throughput - at the expense of increased seek time. Large files will fly, but a bunch of smaller files (or fragmented disks) might move faster on a single unstriped drive. That being said, I haven't noticed anything being slower on my 'software' striped array (WinXP).

l008com · May 30, 2003, 01:17 AM

I also read that while a mirrored raid writes no faster or slower than a single drive, it does read at twice the speed, since the data is there twice, and can read differnet parts from the seperate drives at the same time. But not if they are on the same IDE bus.

Spliffdaddy · May 30, 2003, 01:33 AM

and, yes, folks

you can take 2 hardware RAID 0 cards, each supporting a pair of striped hard drives - and use 'software' RAID to stripe them together into a single ass-kicking disk...that boasts four times the throughput of a single disk.

I haven't tried adding more than 2 RAID 0 cards, bit I'm certain at some point you would saturate the PCI bus.

JB72 · May 30, 2003, 02:38 AM

Originally posted by Spliffdaddy:
here is some general info that might help...

'Software' RAID 0 striping usually requires support from the operating system. For this reason, 'software' striped arrays cannot be made bootable.

Err wait. I used a striped software RAID on my MDD as a boot for a while. It was only a temp test but it worked w/o problems. Currently that set is a secondaty media drive. I'm trying to hold off for the 64bit 4-channel RAID card mentioned in this thread.

Spliffdaddy · May 30, 2003, 11:52 AM

could you take a minute to explain how you got it to boot from a 'software' RAID disk?

Is there a disk utility (outside of the OS) that can format and initialize the array? Or did you have to load the OS in order to set up the array.

I'm under the impression that it would require the motherboard's BIOS (firmware) to be able to recognize the array in order to boot from it.

Otherwise, the boot sector would exist on a single harddrive (physical disk) which the firmware 'points to' during boot - and that would contain the bootloader which could be used to initialize the software striped array. The remainder of the OS system files could then be read from a striped array. Until the ability to recognize, read, and write to a software striped array is given to the machine - it simply can't do anything with it. Unless the BIOS (firmware) itself has this ability - you cannot boot directly from a software striped array.

What you CAN do is place the necessary information in the bootloader (on a single unstriped disk) to support the software RAID - then have it continue the boot process from a striped array. I was able to place all of my WinXP system files on a striped array - but the bootloader still resides on an unstriped disk...because my motherboard BIOS could not 'point to' a striped array. I cannot manipulate 'logical' drives from BIOS...only the 'physical' drives.

I'm curious as to how Apple was able to provide firmware support for software striped arrays. It's certainly possible, but very unlikely.

Camelot · May 31, 2003, 07:58 AM

Originally posted by Spliffdaddy:
could you take a minute to explain how you got it to boot from a 'software' RAID disk?

ALL Macs since the original XServer have been able to boot off a software RAID volume formatted with Apple's Disk Utility software.

The version of Open Firmware in these machines understands how to mount the RAID at boot time.

Earlier Mac models could not (and still can not) boot from RAID unless using third-party RAID controllers that perform hardware RAID functionaility.

JB72 · May 31, 2003, 09:26 PM

Originally posted by Spliffdaddy:
I'm curious as to how Apple was able to provide firmware support for software striped arrays. It's certainly possible, but very unlikely.

Unlikely? Try it for yourself.

"ALL Macs since the original XServer have been able to boot off a software RAID volume formatted with Apple's Disk Utility software.

The version of Open Firmware in these machines understands how to mount the RAID at boot time."

Spliffdaddy · Jun 1, 2003, 12:11 AM

*glances around the room*

nope. I don't seem to have a Mac.

It's a very cool thing that support is offered in firmware for booting a software-striped RAID.

The reason I chose the word "unlikely" is because it is unlikely that very many users would need it...not that it was unlikely to be possible. It's a bonus, of sorts, something I wish Windows offered.
or maybe it does and I just don't know it. I've been wrong before, ya know.

JB72 · Jun 1, 2003, 01:04 AM

Originally posted by Spliffdaddy:
The reason I chose the word "unlikely" is because it is unlikely that very many users would need it...not that it was unlikely to be possible. It's a bonus, of sorts, something I wish Windows offered.
or maybe it does and I just don't know it. I've been wrong before, ya know.

Well now I appreciate it more.

nerd · 10:34 AM

Why is everyone making RAID so difficult? You CAN boot off a striped RAID. I did it on my 8500 using Hard Disk Toolkit and also on my Dual 533 using Apple drivers. The RAID info is installed with the drivers on the drive that gets read when you first boot the computer. Look at a partition map using HDT, you'll see the Apple driver (or whomever you format with) installed on the drive. That simple. Where do you guys get this xServe can only boot RAID? The limit was OS X.1 and earlier and that limit was you couldn't INSTALL X on a RAID (the installer wouldn't show the drive) but if you Carbon Copied a boot drive over to the RAID it would boot it. The 10.2 installer will show and let you select a RAID volume.

I can't speak for RAID 1 but if you guys bug me enough I'll Carbon Copy my server's boot drive to the mirrored drives and see if it boots.

Hope this clears up some things. I'm just telling you guys what I have experienced, not trying to get on anyone's case.

Brad

EDIT:

What I want to know is when somone is going to port over RaidTools from the nix enviroment so we can have software RAID 5. Maybe Apple will provide it but I think that would get in the way of their xRaid sales.

CatOne · Jun 2, 2003, 12:05 AM

Originally posted by Spliffdaddy:
could you take a minute to explain how you got it to boot from a 'software' RAID disk?

Is there a disk utility (outside of the OS) that can format and initialize the array? Or did you have to load the OS in order to set up the array.

I'm under the impression that it would require the motherboard's BIOS (firmware) to be able to recognize the array in order to boot from it.

Otherwise, the boot sector would exist on a single harddrive (physical disk) which the firmware 'points to' during boot - and that would contain the bootloader which could be used to initialize the software striped array. The remainder of the OS system files could then be read from a striped array. Until the ability to recognize, read, and write to a software striped array is given to the machine - it simply can't do anything with it. Unless the BIOS (firmware) itself has this ability - you cannot boot directly from a software striped array.

What you CAN do is place the necessary information in the bootloader (on a single unstriped disk) to support the software RAID - then have it continue the boot process from a striped array. I was able to place all of my WinXP system files on a striped array - but the bootloader still resides on an unstriped disk...because my motherboard BIOS could not 'point to' a striped array. I cannot manipulate 'logical' drives from BIOS...only the 'physical' drives.

I'm curious as to how Apple was able to provide firmware support for software striped arrays. It's certainly possible, but very unlikely.

To do this you just boot off the OS X installation CD, and then run Disk Utility off the CD. Set up a couple drives as a RAID set, and then install the OS on that new (mirrored or striped) disk. Easy.

And if you use a RAID 0 it's FAST to boot. Have it set up with 2 RAID 0 pairs on my 720 GB Xserve... w00t!