SSD cache issue – despite flushing, there is a risk of data loss in the event of a power outage

Based on his own testing, developer Russ Bishop reports that data loss can occur with some NVMe SSDs despite the supposed buffer flushing (cache flushing). This occurred with two of the four tested NVMe SSDs from different manufacturers. Bishop wants to check more.

Backed up cache data will be lost

Bishop, who works as a programmer at Apple, writes on Twitter: “I tested a random selection of four NVMe SSDs from four vendors. Half lose download data during power outages“. What is meant is that the data then the Clear cache (flush) they were lost when in fact they should already have been safely transferred to the memory cells of non-volatile NAND flash memory.

Data is usually only temporarily cached for a short time and transferred to permanent memory as quickly as possible. However, if the behavior observed by Bishop occurs at this very moment, the result is data loss.

that the data in the cache disappearing in the event of a power outage is normal and is due to the volatile DRAM cache in SSDs (alternatively HMB in RAM in non-DRAM SSDs) and can only be avoided with backup capacitors, which are only available in some SSDs business.

However, Bishop conducted his tests with SSDs from traditional consumer customers without such guarantees. The “power failure” was simulated by pulling on the power cord after the successful download was reported.

Fun story: I tried a random selection of four NVMe SSDs from four vendors. Half lost FLUSH’d data on power loss. That is, the wash went to the drive, confirmed, successfully reported all the way back to userspace. I then manually pulled the cable. Boom, the data is gone.

— Russ Bishop (@xenadu02) February 21, 2022

Two out of four SSDs lost data

The two NVMe SSDs that lost data were a 2TB SK Hynix Gold P31 and a 512GB Sabrent Rocket. With a Samsung 970 Evo Plus with 2TB and a Western Digital Red SN700 with 1TB, the written data was preserved.