AST RESEARCH, INC. TECHNICAL BULLETIN # 1055 1-20-95 RAID CONSIDERATIONS WITH AST'S MYLEX DAC PROBLEM A physical disk drive can not be rebuilt (using hot-swap or hot-standby techniques) when using AST's Mylex DAC products. CAUSE When the logical system drive was created, the physical disk drive was not supported by the DAC configuration utility software. PREREQUISITES Due to the comprehensive nature of the DAC subsystem, AST recommends the System Administrator receive proper training prior to configuring this subsystem. This Technical Bulletin assumes the System Administrator has already received training from AST and is familiar with the DAC subsystem. SYSTEMS AFFECTED AST PART NUMBER DESCRIPTION 501453-001 1-CHANNEL EISA SCSI DISK ARRAY CONTROLLER 501133-001 3-CHANNEL EISA SCSI DISK ARRAY CONTROLLER 501133-002 5-CHANNEL EISA SCSI DISK ARRAY CONTROLLER PARTS AFFECTED AST PART NUMBER DESCRIPTION 230624-001 CONTROLLER DAC 1-CHANNEL 230414-003 CONTROLLER DAC 3-CHANNEL 230355-XXX CONTROLLER DAC 5-CHANNEL 221134-001 FRU DAC5 HD CTRL SOLUTION Reconfigure the logical system drive with the release of DAC utility software that supports the physical disk drive. BACKGROUND In order for the hot-replacement and hot-standby features to function properly, all physical disk drives that are being configured as logical drives must be the exact same size. In most instances, when the same manufacturer and model are used, this is not a concern because the drives are usually the same size. It is usually a concern when different manufacturer and/or models are used. AST has qualified 500 megabyte, one gigabyte and two gigabyte disk drives for use with the DAC. AST assigns a single part number for 500 megabyte (230134-500), one gigabyte (230135-132 and 230135-133) and two gigabyte (230135-232) SCSI disk drives. Several different manufacturers and/or models are sourced under each part number. As a result, (using the one gigabyte disk drive as an example) when a one gigabyte disk drive is requested from AST, there is no way to predict who the manufacturer and/or model of that disk drive will be when it is shipped from AST. This is a concern because the size of each manufacturer's one gigabyte disk drive is not always exactly 1000 megabytes. In fact, most one gigabyte disk drives are slightly larger then 1000 megabytes. The actual size of the disk drive as it is delivered from the manufacturer is called the "native" size. For example, the native size of the Quantum 1080s disk drive is 1029 megabytes, and the native size of the HP C2247 disk drive is 1003 megabytes. They both need to be exactly 1000 megabytes in order for the hot-replacement and hot-standby features to function properly. INTRODUCING DRIVE SIZING The native size of each disk drive needs to be modified so that all of the disk drives are the same size when they are connected to the DAC. This process is called "drive sizing". In order for the hot-replacement and hot-standby features to function properly, all physical disk drives that are being configured as logical drives must be the exact same size. AST provides utility software with the DAC to make disk drives with different native sizes appear as if they are exactly the same size. For example, after the Quantum 1080s disk drive has been sized properly, it is seen by the DAC as 1000 megabytes instead of 1029 megabytes. DRIVE SIZING PROCESS The following dialog reviews the drive sizing process: AST provides utility software with the DAC to enable system administrators to configure one or more independent physical disk drives as a single logical disk drive. A "logical disk drive" is commonly referred to as a "system disk drive". During the course of configuring the system disk drive, each physical disk drive provides a drive identification header to the DAC. The identification header informs the DAC who the disk drive's manufacturer is and the disk drive's model number . The identification header is cross referenced to a file called "ID.DAT". The ID.DAT file is cross-referenced to several files with a file extension called "SIZ". The file "ID.DAT" also contains a listing of all the disk drives that are supported by the DAC. Each supported disk drive is listed on a separate line in the file which is exactly 16 characters in length, and corresponds to a file with the extension "SIZ". The files with the "SIZ" extension contain the modified size of the drive. DRIVE SIZING EXAMPLE The following text resides in the example file /DACCFG/ID.DAT: QUANTUM EMPIRE_1 QUANTUM EMPIRE_5 HP C2233-30 HP C2235 HP C2244 HP C2247 QUANTUM PD1050iS QUANTUM LPS525S SEAGATE ST12400N SEAGATE ST31200N DEC DSP3210S QUANTUM EMPIRE_2 HP C3323A The first line contains the SCSI identification header for the Quantum 1080's one gigabyte disk drive. Because the header is located on the first line, it corresponds to the file called "1.SIZ". The text located in the file 1.SIZ is "1000". When the Quantum 1080's disk drive is sized, the DAC does not recognize the native size of the disk drive. Instead, the disk drive is recognized as 1000 megabytes. The sixth line contains the SCSI identification header for Hewlett Packard's one gigabyte disk drive. Because the header is located on the sixth line, it corresponds with the file called "6.SIZ". The text located in the file 1.SIZ is "1000". When the Hewlett Packard disk drive is sized, the DAC does not recognize the native size of the disk drive. Instead, the disk drive is recognized as 1000 megabytes. After both disk drives have been sized, they are exactly 1000 megabytes and can be used in a RAID configuration without any problems. In this example, because two disk drives are being discussed, they can be configured in a RAID 1 configuration and the hot-replacement and hot-standby features will function properly. DRIVE SIZING VERIFICATION It is important for a System Administrator to be able to verify that all of the physical disk drives connected to the DAC are properly drive sized. Following the procedure below enables the System Administrator to verify the disk drives are properly sized: 1. Boot the latest release of the DAC DOS utility diskette. 2. Load the mouse driver that accompanies the mouse that is connected to the computer system. 3. Change to the directory called "DACCFG" by entering the command "CD \DACCFG". 4. Execute the DAC Disk Array Configuration program by entering the command "DAC960CF". 5. Click on the "VIEW/UPDATE CONFIGURATION" button. 6. Click on the "FORMAT SCSI DRIVE" button. The button is located on the lower right portion of the screen. 7. Click on the graphical representation of each disk drive. A box containing several fields will be displayed in the upper left portion of the screen. Each field reviews specifics about that particular disk drive. One field needs to be reviewed to verify the disk drive is properly sized. The first field reads "Capacity [MB] : nnnn", where "nnnn" is the modified size of the drive. For a 500 megabyte disk drive, "nnnn" must be equal to "500". For a one gigabyte disk drive, "nnnn" must be "1000". For a two gigabyte disk drive, "nnnn" must be equal to "2000". The disk drive is not properly sized if "nnnn" contains any other numbers . 8. Click on the "EXIT" button that is located in the upper right portion of the screen, next to the clock. 9. Use the steps outlined above to verify each physical disk drive. 10. After all disk drives have been reviewed, click on the "QUIT" button to exit the menu. DRIVE SIZING RESOLUTION The logical system drive needs to be recreated if one of the physical disk drives is not properly sized. Since recreating a system drive requires reinitializing the system drive, all of the data must be backed up prior to creating the new system drive. The data is restored after the system drive is initialized. Notes 1. It is important to perform a full system backup prior to initializing a system drive because initializing a system drive will destroy all data. 2. Please reference the Disk Array User's Manual for the procedure that explains how to use the DAC Configuration Utility to create new system drives. 3. The latest release of the DAC DOS utility diskette is located on AST's BBS in the Systems file area. The name of the file is "SMP7.EXE". AST's BBS can be reached by dialing (817) 230-6850. AST's BBS supports modem speeds up to 28.8k bps. This file will also be posted on: - CompuServe Go ASTSUPPORT - AST Worldwide Web Site http://www.ast.com