Get the best of all worlds from your RAID setup!

Based on my benchmarking results, it is clear that in the OS X 10.4.7, RAID-1 (mirroring) redundancy does not improve read performance speeds. Furthermore, there are occasions when, such as with video-editing, you simply want the best disk read / write performance you can get out of your system.

Based on my current analysis, I strongly recommend using 4 drives for OS X, and 1 to 2 additional SATA drives for Windows XP. (Yes, there are 6 full SATA ports available on your motherboard. Installing a SATA cable for the spare CD-ROM bay requires non-trivial removal of the metal-covering over the heat-sink and removing the big fans... You might prefer to install a Parallel ATA hard drive to install windows XP on... I’m not yet sure the best way to install 6 SATA drives on the Mac Pro yet).

In my example I have installed 4x 300 Seagate Barracuda version 10 drives (version 10 uses perpendicular recording technologies). I selected this drive because it was relatively fast, used the new recording technologies and because I got them at a great price!

I will first describe the basic layout, the size and type of partitions I selected, and then the steps I used to create the partitions on the drive. This layout of 4 drives is intended only for OS X usage. The Windows XP drives should provide space for FAT-32 file movement.

The OS-X Partition Layout

I suggest, for the OS-X RAID set, you might consider a variation based on the following 3 partition layout:

    * Speed

    * Boot

    * Data

The first partition (nearest to the drive spindle) should be your ‘Speed’ partition (for OS data). The reads and write operations are fastest over this portion of your drive. I recommend the speed partition should be a 4-disk wide stripe (RAID-0). The size? That entirely depends on you. I have selected to build an 80 gigabyte ‘speed’ partition. To achieve this, I will allocate a 20 gigabyte partition on each drive. If you are doing a lot of video editing, you might want a larger drive. (Please, this is a ‘scratch’ or ‘temporary’ drive used for high-performance operations. Be sure to store your important mile-stones back on your robust ‘Data’ partition).

The second partition should be your ‘Boot’ partition. The Boot partition will contain your operating system and personal directories. I believe it is important to achieve both speed and reliability on this partition. I recommend RAID-10, which stripes two sets of mirrored drives.

A RAID-0 striped boot drive is a VERY silly idea. The chances of the striped drive failing increase every time you add a drive. A 4 wide stripe has 4 times the chances of loosing all your harder-to-backup data (such as configuration files, mail, etc). I have selected to build a 60 gigabyte ‘boot’ partition. 60 gigabytes should be more than enough for the core operating system and home directory if you store your larger binaries / data in your ‘Data’ partition. To achieve this, I will allocate a 30 gigabyte partition on each drive. (There is a total of 120 Gigabyte of physical disk allocated, 60 of that is redundancy against catastrophic drive failures).

The third partition should be your slower ‘Data’ partition (for OS X). This is where you should try to store all your music and data files. The thinking is, if you have to reinstall the operating system, you can reformat the ‘Boot’ partition, but leave most of your data in one place. I would normally recommend RAID-5 (n disks data, +1 disk for redundancy), but OS X 10.4.7 desktop does not offer software RAID-5 to its users. RAID-5 would increase the amount of storage space available, while maintaining protection from any single disk failure. Thus, I recommend RAID-10. I will allocate all remaining space to my ‘Data’ partition. I hope that the Apple marketing team decide that the Mac Pro deserves RAID-5 on the desktop models of the operating system.

Sourcing the Disks

When building a professional RAID system, it is highly recommended to source identical drives (Size, Cache, Model Number and potentially BIOS revision). While the physical characteristics of the drive should be as close to identical as possible, it is advised to purchase drives that were built in different manufacturing batches. The reasoning goes, you don’t want 2 drives from the same faulty batch to die on you at very nearly the same time! If you are unsure about how to determine the batch number, you might try one of the following:

    * Purchase each drive from a different distributer (rely on chance)

    * Purchase your drives at different times (a week, two weeks apart from a high-volume distributer) (again, relying on chance)

    * Ask your hardware distributer if he can source drives from different manufacturing batches suitable for use in a RAID (may cost you more time and money).

When selecting your drive, please consider your application. If you are sensitive to noise, you may want to source the quietest disks in preference to the worlds fastest drives :)

Wrangling with the Disk Utility

In Raid setups, not only do you want identical drives, but you want the partitions for a RAID set to be located in the same physical location on the disk. This is easily achieved in practice. The Disk-Utility tool by Apple lacks a certain degree of user-interface precision when calculating the exact partition sizes. I will describe is a simple process that ensures you get the right-size and right-position for each partition.

First, you will need to boot from the CD-ROM installation disk, and use the Disk Utility accessible through the pull-down menu ( Select [Utilities] / [Disk Utility]... ) before you install the operating system. (If you are having difficulty booting from the CD-ROM, hold the ALT key down when your system is first rebooting until a screen offers a selection of “boot partitions”; select the cd-rom.)

Second, calculate the physical partition / volume sizes for your 4 drive RAID setup.

    * 80 Gigabyte ‘Speed’ partition, RAID-0     = 80 / 4 = 20 Gigabyte per partition

    * 60 Gigabyte ‘Boot’ partition, RAID-10    = 60 / 4 = 30 Gigabyte per partition

    * Remaining ‘Data’ Partition, RAID-10    = What-ever is left.

Third, for each drive, create in sequential order, from top down, the partitions you want.   When selecting a drive, carefully review the ‘bay-name’. We will select the xxx_1, xxx_2 extension by the bay-name.

So for the drive with Connection ID: “Bay 1”:

    * I will create a new 3 volume scheme; then

    * create a 20 Gigabyte volume, format: Mac Os Extended (J), and call it Speed_1; then

    * create a 30 Gigabyte volume, format: Mac Os Extended (J), and call it Boot_1; then

    * format the remaining volume with Mac Os Extended (Jour...), and call it Data_1; then

    * Hit the ‘Partition’ button down the bottom-right, to commit the layout to disk.

Repeat for each of the four drives, ensuring the extension number matches the Bay id.

The exact size of the partition will most-likely not be the number you entered. This is very normal for partitions (low level black-magic), regardless of operating systems. What we do want to check, is that the exact size you have been allocated is the same across every drive.

Firth, now that we have created the basic place-holders for our three logical RAID volumes (speed, boot, data), we want to build our RAID set.  It is best if this step is performed before the operating systems is installed.

For RAID-0 ‘Speed’ partition, we select the Speed_1 volume in the left hand scroll panel, and then select the RAID Tab. We set the RAID Set Name as ‘Speed’. The volume format is left as Mac OS Extended (Journaled). Raid Type is Striped RAID Set. We drag the Speed_1, Speed_2, Speed_3 and Speed_4 partitions into the large list box. The names of the partitions will change from Speed_1 to incomprehensible tech speak “disk1s2”, etc. When you have the four volumes present in the Raid Set, click ‘Create’ twice.

For RAID-10 ‘Boot’ partition, based loosely on the steps followed above, we need to create three RAID volumes:

    * Create a Mirror RAID of Boot_1 & Boot_2, called ‘Boot_a’

    * Create a Mirror RAID of Boot_3 & Boot_4, called ‘Boot_b’

    * Create a Striped RAID of Boot_a & Boot_b, called ‘Boot’

        (I have found, that when striping RAID volumes, you may need to hit the [+] Button first to create a node that the Boot_a, Boot_b volumes can be dragged into.)

For RAID-10 ‘Data’ partition, we need to perform three steps:

    * Create a Mirror RAID of Data_1 & Data_2, called ‘Data_a’

    * Create a Mirror RAID of Data_3 & Data_4, called ‘Data_b’

    * Create a Striped RAID of Data_a & Data_b, called ‘Data’

        (I have found, that when striping RAID volumes, you may need to hit the [+] Button first to create a node that the Boot_a, Boot_b volumes can be dragged into.)

I have personally noticed that the building RAID sets doesn’t work every-single time. If it does not appear to be working, cleanly reboot the system via software, boot from the Installation disk, and try again from in Disk Utility.

From here, your system will show only 3 drives: Speed, Boot & Data.

Sixth, install your OS X operating system on the ‘Boot’ partition.

~~~ Party! ~~~

Question: Why RAID-10

Answer: Very briefly, RAID-10 accelerates both READ and WRITE operations. This is excellent for data-bases and anybody doing a lot of music or video production work. RAID-10 has a similar physical cost as simple mirroring (RAID-1); a full 50% overhead. A 4 disk RAID-10 configuration will operate under any single drive failure, and some (but not all) 2 disk failures. RAID-5 is cheaper than RAID-10, it only accelerates READ operations, and its not currently available in OS X desktop.

Perspective: you spent a lot on your base system and hard drives are your slowest component and are much cheaper to purchase than Mac Pro RAM! If you really need the space, get 4x750 Megabyte drives, and RAID-10 them. Its probably cheaper than buying OS X Server just for the RAID-5 functionality.

Last Updated: 2009 November 15