[opensuse] PCIe disks V. SATA/SAS disks (was Re: Get an SSD just for swap?)

Greg Freemyer wrote:

On Sat, Dec 2, 2017 at 7:40 PM, L A Walsh wrote:

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The benchmarks are for SSD-drives that take the place of hard-drives -- not motherboard attached ramdisks.

NVMe SSDs are current generation hard drives. They aren't ramdisks in any sense of the word. I bought my first one 2 years ago.

I've been looking at options for a replacement PC (old one died, ~2 years out of warranty and soldered-on BIOS became corrupt (joy!)). Reading a user guide (https://docs.broadcom.com/docs-and-downloads/host-bus-adapters/pub-005851_20... or https://tinyurl.com/ycnxbkjz) for one of the disk adapter options: a Broadcom (LSI) MegaRAID + HBA card that explicitly supports Tri-mode operation. (Tri=SAS, SATA and PCIe). They describe the supported speeds: • SAS data transfer rates of 12Gb/s, 6Gb/s, and 3Gb/s per lane • SATA transfer rates at 6Gb/s and 3Gb/s per lane • PCIe (NVMe) data transfer rates of 8 GT/s, 5 GT/s, and 2.5 GT/s per lane Of note: the PCIe "disks" list speeds in terms of memory transfers, not the Gb/s of SAS or SATA disks. I submit that they *are* non-volatile ramdisks in _most_ senses of the word. I don't see why that is a bad thing, it allows them to have memorythough it would exclude them from sites that are only focused on SATA/SAS based SSD hard drives. The speed-unit of "GT/s" (Giga-transfers/second) is the same unit used for accessing non-local-node NUMA memory. For multi-socket MB's, each socket has it's own memory. Accessing non-local comes at a noticeable cost -- on the order of 1.5x - 3x. PC's from ~7 years ago operated in the 4.8-6.4GT/s (Giga-transfers/s) and are now up to 10.4GT/s in current processors. That gives a comparison point to PCIe's 2.5 - 8 GT/s. That's likely to give around 2GB/s (I get up to a bit over 1GB/s with HW RAID using 7200RPM disks using a 3Gb/s bus speed (older generation computer). The random perf differences of the PCIe cf. my RAID, would likely be a few-to-several times greater than the linear. So much faster (and maybe replacing conventional HD's for PC's, but w/RAIDs still used for capacity -- at least for a while. -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org