HGST drives in RAID arrays

    Good afternoon, friends and colleagues. Today we would like to talk about the advantages of using HGST drives in RAID arrays and how our solutions help ensure the smooth operation of data centers, minimizing financial and reputational risks.

    Enterprise users prefer to configure systems with RAID arrays for reliable data protection, minimizing downtime and maintaining performance. That's why they choose HGST enterprise-class drives that deliver best-in-class reliability, consistent throughput and power. However, even the most reliable drives in the world cannot completely eliminate the risks of data loss. RAID systems have come a long way to minimize these risks, but nonetheless, the recovery processes that occur as a result of a disk failure are still inevitable. In this regard, a number of problems arise: the loss of time, performance and data security are tasks that HGST plans to cope with thanks to the Rebuild Assist function.

    No storage technology is immune from errors. The drive and flash memory may suffer from misuse.

    HGST uses a number of diagnostic functions to evaluate possible errors, information about which is sent to the RAID controller for further analysis and identification of possible corrective actions.
    HGST drives minimize the possibility of errors, as evidenced by the average time between failures of 2 hours. Minor errors can often be corrected or redistributed, which leads to the absence or minimization of data loss. However, a data-filled disk may show significant errors that can be identified as a disk failure. In this case, the RAID controller must take measures: disk errors will be transferred to standalone operation, and the array will be placed in limited functionality mode to reduce the possibility of additional data loss as a result of a long-term malfunction. While the data is reconstructed in a reinstalled or hot-swap drive, the RAID controller continues to provide access to the data.
    And it really works. The disadvantage is that restoring the contents of a disk can take a long time. Despite the fact that the array is running in a slow state, it must restore the data and at the same time still respond to their requests. In terms of performance, RAID configurations are often used as shared storage. This means that the decline in productivity caused by recovery can affect the productivity of many workers.

    Rebuild RAID. Not all RAID users understand how high the risk of data loss is that is possible with a secondary failure during the recovery process. Reducing recovery time can reduce this risk.

    Why is tuning time increasing

    At a time when the capacity of arrays was measured in megabytes and gigabytes, the time required for rebuilding RAID arrays was considered acceptable. Nevertheless, the practical consequences of switching to terabyte arrays quickly become noticeable, given the basic formula for calculating the time required for tuning:

    Capacity (Mb) / Average data transfer rate (Mb / s) = Tuning time (s)

    When it comes to rebuilding a 3TB volume on a regular 3.5-inch hard drive with an average data transfer rate of 110 Mb / s, rebuilding will take 19,108 seconds (or 5.3 hours). This is a typical situation for a RAID 1. If this doesn’t scare you, then remember that more sophisticated arrays work in “limited functionality mode” when one of the drives is disconnected. This reduces the performance of volumes and further increases the rebuild time. In practice, the RAID 5 rebuild speed can easily drop to around 10Mb / s, so this process will take days, and this is unacceptable for most data centers that must follow certain guarantees for the level of service for end users.

    As disk capacity grows, both rebuild time and risk of data loss increase. For example, using a rebuilding time estimation program for a RAID 5 array consisting of 12 disks with one quick automatic backup enable device consisting of 3TB disks versus 5TB disks and a decent rebuild speed of 40Mb / s, it can be established that the annual probability of data loss by 54% higher on a 5TB more capacious disk array, mainly because rebuilding will require about 13 hours more *. If a second disk fails in a RAID array that does not provide additional redundancy, the contents of the volume will be lost, often irrevocably. RAID 6 is often used to reduce the risk of a second drive failure.

    * The example was simulated using the tuning time calculator located at: www.memset.com/tools/raid-calculator

    Modeling conditions: average data transfer rate 40Mb / s, 12 disks in the array (including a parity disk and a device for fast automatic reserve switching) , a five-year warranty and the ability to replace the disc within 7 days.

    Summing up, it should be noted that there is a direct relationship between the disk capacity and the tuning time, or more precisely, the larger the capacity, the longer the tuning process takes under conditions of operation in the mode of limited array functionality. To solve this problem, HGST has provided Rebuild Assist, which meets all industry standards, on its latest enterprise devices. It not only reduces the time required to rebuild arrays, but also reduces the risk of data loss, quickly restoring the full operability of the array.

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