New 840 EVO fix adds ''periodic refresh'' to firmware

Last year, some Samsung 840 EVO SSDs started exhibiting slower read speeds with old data. The problem was patched in October, but the fix didn't stick, with slowdowns returning months later. Samsung pledged to release another fix in March, and now, that update is scheduled for "later this month."

Since the EVO's slowdowns manifest over time, we won't be able to verify the effectiveness of the new patch right away. However, we can share some details about what the incoming fix entails. Here's what Samsung told us when we asked for specifics about how the new firmware addresses the cell voltage drift that seems largely responsible for the problem:

• Samsung revised the firmware algorithm to maintain consistency in performance for old data under exceptional circumstances. Therefore, read performance was restored without the need for Magician. This algorithm is based on a periodic refresh feature that can maintain the read performance of this older data. The algorithm does not affect normal user scenarios (i.e. occasional PC performance degradation due to background work of SSD) or the lifespan of an SSD and can actively maintain its performance without the help of Magician. However, this algorithm does not operate when the power is off.

• The read performance has been improved by the revised firmware algorithm. If performance recovery is slow in instances where the SSD did not have enough run-time for the firmware algorithm to reach normal performance levels, or similarly, had been powered off for an extended amount of time, the performance can be recovered by using the Advanced Performance Optimization feature in Magician 4.6. This is a supplementary feature to maintain normal performance for a few exceptional circumstances.

• Users can upgrade to the new firmware through Magician 4.6, without using the performance restoration tool.

Interesting. When users first encountered slowdowns with the EVO, they found that rewriting the old data brought reads back up to speed. It sounds like the new firmware's "periodic refresh feature" does something similar.

The refresh routine appears to run in the background, when the drive is idle, so it shouldn't affect performance in normal scenarios. Refreshing old data may consume some of the NAND's limited endurance, though. We've asked Samsung to clarify how frequently data needs to be refreshed and how this affects write amplification.

Since old data can only be refreshed while the drive is on, those who leave the EVO unpowered for extended periods will have to rely on the Magician software's optimization mechanism if they want to restore full performance quickly. It's unclear how long the EVO will take to optimize itself after extended downtime.

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