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[ESXi 6.5] Write speeds on NVMe datastore (Samsung SM961 256GB) have dropped from 1400 MB/s to 360 MB/s even with only one VM running. Any way to restore write speeds?

[ESXi 6.5] Write speeds on NVMe datastore (Samsung SM961 256GB) have dropped from 1400 MB/s to 360 MB/s even with only one VM running. Any way to restore write speeds?


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5 Comments

  1. Definitely look into TRIM, I believe it’s enabled by default on with non-aggressive settings on 6.7 if you’re using the latest version of VMFS. You’ll have to manually run it on 6.5 IIRC.

    This may also just be expected behavior since this kind of drive isn’t designed for the kind of workload that you’re giving it. Your drive likely is blowing through it’s super fast SLC cache, leaving you with the moderately fast TLC NAND. This is how they can pack so much “bursty” performance into a cheap drive.

    “The SM961 will not offer a large performance increase under very light workloads. However, when you ask for high-performance the SM961 will deliver, while the TLC-based SSD will drop to native NAND speeds when it exhausts the SLC cache. It may be difficult to imagine, but the SM961 will provide a 10 to 15x performance increase over TLC drives when writing large volumes of sequential data. That’s a bigger difference than comparing the first consumer SSDs to hard drives.”

    The screenshot that you posted only includes the sequential test from CrystalDiskMark, which honestly isn’t an accurate benchmark unless all of your workloads are sequential. Even then, your drive will drop down to TLC NAND speeds pretty quickly.

  2. This NVMe drive came with my Lenovo workstation. I am running ESXi on it so decided to use this drive as an additional high speed Datastore. Initially write speeds were up around 1300 – 1400 MB/s running Crystal Disk Mark from one of the VMs on that Datastore but after a check today (6 months later) they seem to have dropped drastically.

    ​

    I tried Googling “esxi trim” but I didnt find anything conclusive about whether ESXi 6.5 uses it or how I can manually trigger it if it does.

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