Stop! Is your low-cost Christmas upgrade a disaster waiting to happen?

Disk drives turning into SSD drives

Posted on Tuesday, December 19, 2017

As the cost of SSD drives falls, many CTOs may be preparing to upgrade their existing arrays by replacing the magnetic hard drives with flash. Such a move should deliver an instant speed boost, helping to reduce data access times.

However, there’s a potential problem with this concept.

The finite lives of SSD

Flash memory chips have a pre-defined lifespan of approximately 1 billion writes. Once that threshold is reached, the drive switches to read-only mode, so data can be copied to another, working unit before complete failure.

For the CTO, the predictability of SSDs is great news, making it very easy to schedule replacements before drives fail. But this could be a major problem in a RAID array.

When all your drives fail at once

RAID arrays are designed to complete write operations across all drives simultaneously, helping to balance workloads. But where the array is populated with flash drives from the same production batch, there is a genuine risk that they will all fail almost simultaneously as they each reach their write threshold at the same time.

Data will not be lost should this happen, but operations will need to be halted until the drives can be replaced and the array rebuilt from scratch.

Two potential solutions

The easiest, lowest cost solution to the challenge is to ensure that all SSDs come from different production batches. It may be that you need to source drives from different resellers, or the chances of receiving concurrent serial numbers is highly likely.

The alternative is to ask your vendor about solutions that could potentially “unbalance” write operations. This will then ensure that wear on each drive is different, and that they do not fail simultaneously. These technologies are apparently quite rare however, so your OEM may not be able to help.

Flash is indeed the future of on-site data storage, but it may be that your business needs to wait a little longer to adopt it. For more help and advice, please get in touch.

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