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January 2000

Arco DupliDisk IDE RAID 1 Controller and OS/2

By: Richard Clark

Yes there is a great hardware-software combo for IDE Drives in using RAID 1. I feel we all have at one time or another built our OS/2 Desktop up to where it was the way we wanted it and in most cases loaded some new software to where we really ended up messing it up so that we had to start all over again. Backing it all up by tape is still a good thing, but I feel using this IDE RAID is a big plus over that. For those using or thinking of buying a CD-Writer just for backups, I would advise serious consideration of this unit.

The unit sells for around $230US give or take, which includes the hardware and software. My unit was purchased at Micro Warehouse (http://www.microwarehouse.com). I first became aware of it from an article on it in one of the major computing magazines note 1. Overall it was given an excellent review except for one negative comment that it does not run from a main operating system like Win-98. This negative I feel, to a more open minded reviewer, should have been a big positive, for the full software is run by DR.DOS on one single 3 1/2" disk, run from a floppy drive, that does not depend on any other operating system to carry out the work. The setup works under DOS, OS/2 Warp, Win-3.1, Win 95-98, Win-NT, Netware,Unix, BSDI, and Linux. The hard drives do not have to be the same make or size, but the smaller drive will set the limit. The DupliDisk has automatic drive switching in case of a drive failure, you can choose which way to mirror and shut off mirroring when wanted.

Arco offers several different variations of the controller. There are two different bay mount models (3.5" and 5 1/4"), also PCI and ISA slot models, and a slot less model as well. Since data is actually controlled by your existing IDE controller, no additional IRQ or or I/O address is required. In fact no driver is required other then that used by the operating system for native IDE support. According to Arco the current maximum speed is U/DMA 33, though these controllers will work with ATA/66 controllers/drives, but only at the U/DMA 33 speed. Each controller supports up to two pairs of mirrored drives and will support any drive size supported by the system's IDE controller and operating system.

I installed the unit in a self-built Intel 500 mhz P-III [will upgrade in 2000 to a 750-800 MHZ processor] , with 32-RAM ,LS 120, and a 20 G Tecmar Tape drive and a 52X Kenwood CD, 2-OS/2 OS [one as main and the other for testing] and Win-98. My drives are called Ultra IDE by Maxtor, and I did some homework before selecting Maxtor, of which I had never used before, and was given a high rating for them. I was also told that they put off far less heat than most other drives. I felt with two drives, that this became an important factor.

Installing the ARCO IDE RAID 1 UNIT

Arco calls the Duplidisk an "intermediate adapter design" in that it is cabled between the system IDE drive adapter and the hard drives. It intercepts the data written to the IDE interface and writes to two drives simultaneously, so that each drive is a "mirror" image of the other.

On my installation, I am mirroring to two 17.2 G Maxtor hard drives. Both hard drives must be set as "Masters" on the drives themselves. From my system's motherboard "Primary" IDE Drive Controller, I ran the drive cable to the "Host" connector on the RAID unit. Then from the RAID unit, a primary cable goes to your primary hard drive. Then another cable is put into the mirrored connector on the RAID adapter and to my mirrored drive. It should be noted that I bought a unit that fits in my front bay, but it can be mounted in the rear of the CPU and comes about a third way in as I remember. Except for the cables, the only other item that you will need is a regular plug from your power supply.

The instructions specify to have your CMOS(BIOS) IDE settings for "AUTO or AUTO DETECT", and this is where my only problems were. I set my CMOS settings for the drive detection to"AUTO" and on booting with the disk, was unable to go anywhere. I in turn put "NONE" on all except my primary "Master", and from then on everything has run "Super".

After that the next step is the primary and mirrored drives must be initialized, which is a non-destructive initialization and will not erase any data. Even if both drives are new and have no data, you must still do a "copy data". I asked the company if taking out a drive and putting it directly into another system, if anything with the "initialization" would have be redone first, and I was told nothing would have to be changed.


It took over 2 hours to mirror my primary drive. The RAID setup program indicates progress during the copying operation, and shows the number of blocks to be mirrored (33,708,229 blocks for my primary drive). Upon completion of mirroring, it told me that it was "successful" and "identical", and my "head and cylinder" data was identical. There are a number of choices on the main menu screen, of which I have chosen to have "mirroring" off for now as I will be loading a lot of programs and will re-mirror when I have added several program and feel all is running smooth, then shut off mirroring as I add more programs. Besides controlling mirroring, you can select different disk copying schemes, including

Primary master to mirror master
Mirror master to primary master
Primary slave to mirror slave
Mirror slave to primary slave
Rebuild drive marked as bad

In addition you can do various selective unitialization of the IDE RAID setup as well as comparison of data between drives in mirrored drive groupings (between the Master drive and Master mirror; or between the Slave drive and Slave mirror).

Arco states in their online FAQ (http://www.arcoide.com/faq.htm) - " data transfer speed is controlled by the existing IDE controller on your motherboard. The DupliDisk does not have any effect on drive throughput. It will not slow down the system." and "There is no pause. Because data is written to both drives at the same time, writing to two drives causes no delay.". I have not done any bench tests, but don't get any feeling that anything is slower with the unit installed than without it.

The lights on the front of the unit were helpful for me in making changes to my CMOS settings and give added assurance when you are mirroring from drive to the other. When data is being transferred, the light will go from a green to a orange color. Also when the Status LED is red, you know you are in the single mode or copy is in progress , while green indicates to you that you are in the mirror mode. You could operate from the PCI SLOT or just mounted in the cabinet or such if all bays are in use, but the bay setup makes it easier to know what is taking place, as the lights are in easy view.

With a late model 17.2 G IDE hard drive selling at under $200., I am going to get a third drive to mirror to and put it in another computer that I have. I have nothing what so ever to do with the company and write this because I feel it is one of the best new "hardware-software combo's" to become available to the client-small business, and too few know of it and how it can make our lives a little easier in either a hard drive crash or when we really foul up our drive data.

For more on Arco's IDE RAID controller's there is an FAQ on their site - http://www.arcoide.com/faq.htm which answers common questions about these products. The company is Arco Computer Products, Inc., website http://www.arcoide.com and telephone #: 954-925-2688.

DupliDisk 5 1/4" Baymount - $239 at MicroWarehouse - http://www2.warehouse.com/product.asp?pf%5Fid=EX9701

RAID 1: There are several variations of RAID(Redundant Array of Independent Disks). RAID 1 is the mirroring of one drive to another so that both drives are exact images of each other. That is, when data is written to disk, it is simultaneously written to a second drive. If the primary drive has a physical failure, no data is lost, since the exact same data is on the mirror and the mirror drive takes over. This is known as "Fault Tolerance". However if a software error results in bad data being written to the master, the exact same bad data is also written to the mirror, so continuous mirroring is not a replacement for backing up your data to another media (hard drive, tape, removable drives, CDR).

Note 1: The magazine was PC Computing-May 1999, page 110 under the write up heading "Cover Your Assets" by P.J. Connolly and they gave it their highest rating of 5 stars. http://www.zdnet.com/products/stories/reviews/0,4161,396993,00.html

OS/2 Believer*Richard Clark owns and operates an agricultural operation that has been written up in National Magazines like INC Magazine and was featured on the front page in the upper half of the Sunday Edition of the Washington Post. He built the above system from the ground up using no manual or anyone's help on it. And of course he runs OS/2 on this machine.

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