INDeX Technical Tip. Tip No: 234 Release Date: 20 August 2004 Region: EMEA & APAC. EVM Raid Information. Overview. RAID 5 Stripe Set with Parity

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1 INDeX Technical Tip Tip No: 234 Release Date: 20 August 2004 Region: EMEA & APAC EVM Raid Information Avaya have been made aware that the operation of the RAID controller in the EVM60R voic s requires clarification. Due to the critical nature of the RAID controller, caution should is required when using these applications. Overview Currently the RAID controller installed in the EVM60R is the MYLEX AcceleRAID 170. The server is equipped with three discs configured in a RAID 5 Stripe-set with Parity. The operating system (in this case NT4.0), will report these hard drives as a single physical drive with either one or two partitions. RAID 5 Stripe Set with Parity The operation of the RAID 5 stripe set is based on a parity check. The minimum number of discs for this configuration is three, and the space redundancy is equivalent to one disc. When all discs are working properly, the parity bit is maintained. If a disc fails and is replaced, the controller is aware that the parity bit is out of alignment and will regenerate the information on the new disc to regain the stripe set. However if a second disc fails before the first disc has been recovered, the parity bit check will fail causing the logical drive to lose consistency and the server will halt. It is important to remember that when ordering any replacement drives that they should be the same size and specification as the installed drives. Maintenance It is important to regularly check the discs for correct operation to ensure that any faulty drives can be replaced as quickly as possible. This would minimise the danger of a second drive failing and the loss of the stripe set. Using the software package detailed below, regularly check the discs for errors or failures. The interval for checking this would be dependant on how critical the system is rated and how much load the system is under. A minimum of a weekly check should be performed on all systems. If a drive has been identified as failed by the controller, then the controller will take this drive offline automatically. It would be advisable to confirm via the application which drive has failed. The drive can be removed and a replacement inserted into then old faulty drives slot. The controller will then rebuild the stripe set onto the disc. During the rebuild process, the hard disc activity will increase significantly, and there may be an increase in the normal hard disc access time. It would be recommended that the replacement disc be installed at a comparatively low load time for the voic (evening or weekend) in order to minimise the load on the system. Page 1 of 7

2 Replacing a failed hard drive while operational The three drive bays are locked when shipped from Avaya, the keys will have been supplied with the unit when new. Each bay has two LED s indicating the current state of the drive. Using the Global Array Manager, or the LED s on the drive bays, the failed disc can be identified. The operational discs will show hard disc activity, the failed disc will not show the same activity. Once identified, use the key to unlock the drive. The front cover will hinge forward and allow access to the caddy. Pull the caddy from the enclosure using the folding handle. The hard disc is secured to the caddy with four screws; note that the connection at the back of the disc is virtually flush with the edge of the caddy. Ensure that when the new disc is secured into place, the connector edge is again flush with the caddy. When the drive is replaced back into the drive bay, check that the disc is firmly seated so that the SCSI connectors make complete contact. On detecting a replacement drive in the drive bay the RAID controller will automatically begin the rebuild process. This process may take several hours to complete (depending on the amount of data to be rebuilt) and will increase the load on the remaining discs during this time. It is recommended that this be performed when the voic is under the least possible load. It is considered good practice to carry a Cold Spare hard disc, as a direct replacement should an original fail. Installed Software Supporting the RAID Controller There is controller specific software installed on the server to enable the RAID controller to function correctly and to report information via the operating system. Mylex Global Array Manager The program being used to monitor and modify the controller from within windows is called the Mylex Global Array Manager, and is found in the Start Programs section. When this application is started initially the following screen will appear. Because no controller has been signed onto, the application will display the red X on the left of the window along with a red light indication. Double click on the red cross and the following pop-up screen will appear. Page 2 of 7

3 Ensure that the username is GAMROOT and enter the password NMYSBH. If the check box for the Remember Password is ticked, when the application is closed and re-opened, the controller will not prompt you for a username and will automatically sign on to the specified controller. Upon entry of the correct password, the following screen should be seen. From this point the RAID controller is available for configuration, and the icons on the toolbar will become active. In order to see the current array status, double click on the grey box with DACs(1). This will bring up the following screen. Page 3 of 7

4 Top Circle This shows the current hard drives size and status (Green = OK ). The discs are shown from top to bottom indicating the SCSI ID for each disc (0, 1, 2 ). (More detailed individual disc information is available and is covered later on.) Middle Circle This is showing the controller these drives are attached to, notice SCSI ID 7 is reserved for the controller. Bottom Circle This shows the Total Physical, and Logical capacity for the drives. The available Logical disc size is correct when using RAID 5 Stripe Set with Parity. Above the lower circle is the Logical Drive section, this indicates how the operating system perceives the drive arrangement. In this case Disk Administrator in NT4.0 will report a single disc as Drive 0 = MB. Individual Disc Information The exact make and details of the installed hard discs can be displayed by double clicking on the icon of the relevant disc as shown in the above screenshot. A screen similar to the one below will appear. Page 4 of 7

5 This screen displays the Make, Model, Serial Number and Size of the hard disc. This information is required when holding redundant spares. The screen also shows any errors that the controller has experienced when accessing the disc. Controller Configuration From the Global Array Manger Controller view, double clicking on the controller ( SCSI ID 7 )will display the current settings. This displays the Controller type and firmware version and general information about the current hardware settings. To display the configuration information, click on the Controller Options button. Page 5 of 7

6 The Enable Automatic Rebuild Management option should already be ticked. With this option enabled the rebuilding of a failed drive will be automatic upon insertion of a good drive in direct replacement of the faulty drive. This is dependant on the replacement drive being exactly the same specification as the failed drive. The time taken by the controller to rebuild the stripe set on a new disc varies with disc size and amount of used space on the Logical drive. The operating system may experience a slight increase in seek time during this rebuilding process, and the remaining discs will be under an increased load during this rebuild process. Be Aware: Modifications to the configuration of the RAID controller should not be performed. The Global Array Manager software enables the modifications at a very low level of operation, and mistakes made in this application, may have to be repaired by entering the RAID BIOS, which would involve shutting the system down. The current configuration has been set up to enable the continual running of the EVM system with the simplest method of fault repair. Drivers Installed The Global Array Manager (GAM) works via the SCSI driver installed in NT4.0 and is displayed below. The system is shipped with this driver already installed. Page 6 of 7

7 Documentation Further information and technical documents on the MYLEX AcceleRAID Controller are available from the LSILOGIC website: TERMINOLOGY RAID: Redundant Array of Inexpensive Discs. RAID Parity check: Two state logical Boolean check. In the case of RAID the software is striped across the discs and an extra bit put in to confirm the state. When a disc fails, the Boolean check can calculate the state of the missing bit. However this only works if one bit is missing, if two bits are missing (a second disc fails prior to a complete rebuild), then the state cannot be recalculated and the whole stripe set will fail. SCSI: Small Computer System Interface. This is a faster, more advanced method of disc access compared to IDE. Cold Spare: A new replacement drive of matching parameters being held ready for use. Issued by: Avaya SMBS Tier 4 Field Support Group Tel: +44 (0) Fax: +44 (0) Website: gssfsg@avaya.com Page 7 of 7