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Troubleshooting RAID Failure - CompTIA A+ 220-1101 – 3.10

Let’s have a look at how to troubleshoot RAID failures. Download PowerPoint: https://itfreetraining.com/handouts/a... Redundancy Most RAID systems, but not all, have redundancy. This means that if one storage device in the RAID fails, the failed storage device can be replaced and the RAID will rebuild itself without loss of data. RAID 1 gets its redundancy from keeping a second copy of the data. RAID 5 gets its redundancy from storing parity. There are many different ways parity is calculated – a common method is to count the number of 1-bits and set the parity based on the count being odd or even. When a storage device fails, the 1-bits are counted on the remaining devices and compared with the parity value. This tells the RAID if the missing drive was a one or a zero. Not all RAID have redundancy, for example, RAID 0 has none. If you lose a storage device, you lose all the data in the RAID. If you have a storage device fail in a RAID, you should replace it quickly. Before you do so, make sure you check that cabling is not the problem. If a cable comes loose from a storage device, the RAID may think the drive has failed. This can cause the RAID to go out of sync. When this occurs, your RAID made need to rebuild itself in order to get back in sync. When replacing a storage device, make sure you don’t unplug the wrong one. If you do that, you risk the RAID controller thinking the storage device has failed and you may lose all the data in the RAID. Let’s have a look at how to replace a storage device in a RAID system. RAID Failure Demonstration For this demonstration, I have set up a computer with two hard disks. These two hard disks have been set up to use RAID 1. RAID 1 is also called a mirror, because each drive contains identical copies of the data. I have configured the RAID in the computer’s setup. Thus, this RAID is using motherboard RAID not a dedicated RAID card. Regardless of which solution you use, the principles of how to set it up and use it remain the same. Dedicated RAID cards generally perform better, have more features, and may also have a better interface. To see what RAIDs I have set up, I will select the option, “Select array”. Even though there are two hard disks in the RAID, the RAID will only show one. This is because a RAID is essentially one group consisting of a number of different storage devices. The level of RAID is shown as RAID 1. There are two hard disks having identical data; thus, I have redundancy for a single drive failure, but the cost is my available storage is reduced by half. To look at what storage devices are in the RAID, I will look at the option, “View Associated Physical Disks”. This interface is not very intuitive, meaning it is not easy to understand how it operates if you have not used it before. Both hard disks are working and functional, although the interface shows them as disabled. This discrepancy occurs because the interface is designed to display the properties of individual storage devices, and this does not reflect their current operational status. To view the properties of each disk, you must manually select and enable them within the interface. If this is confusing, think of it as selecting the device rather than enabling it. Yes, the interface is confusing. Therefore, I will proceed by enabling the first hard disk, which is essentially selecting it, then view its specific properties through the option, “View Physical Disk Properties”. This will show the hard disk properties, including if it is currently in use. To see the other hard disk properties, I will disable the first hard disk and enable the second one. With the second hard disk enabled, when I select the option “View Physical Disk Properties”, the properties for the second one will appear. As I said, the interface is not easy to understand. Enabling the device is effectively selecting it. Description too long for YouTube. Please see the following link for the rest of the description. https://itfreetraining.com/ap11/3c30 References “The Official CompTIA A+ Core Study Guide (Exam 220-1101)” pages 105 to 107 “Mike Myers All in One A+ Certification Exam Guide 220-1101 & 220-1102” pages 364 to 365 Credits Trainer: Austin Mason https://ITFreeTraining.com Voice Talent: HP Lewis http://hplewis.com Quality Assurance: Brett Batson https://www.pbb-proofreading.uk