Hacker News Reader

Comment by JoshTriplett | Hacker News Reader

I can understand why, historically, it made sense to have something that looks like a hardware disk but uses RAM. But today, what's the use case for this, versus just adding the RAM to the system directly and using a software RAM disk? That avoids the disk protocol entirely, and should provide substantially better performance.

View on HN

I'd think the main benefit these days might be cost savings from using RAM that's a generation or two older, but in general I think the use case for these hardware RAM disks is probably pretty slim nowadays.

Even with older RAM, if you need a large and fast storage, few solutions can compete with RAM. Especially when it comes to random R/W. You can get 4.4GBps random read from a DDR3 drive (in parents link) while the latest Gen5 NVME drives tend to cap out at ~90MBps for such loads (worst kind of loads). In addition these can be installed into any system, no need for a special server MOBO with enough RAM slots.

What poor NVMe are you buying that gets 90MB/s? Even the Gen3 Kingston 256MB drive I have does well over 500MB/s in my iozone tests on a Dell Precision 3420. The only time you need mobo support is if you want to boot off NVMe but every PCI-compliant OS should be able to at least see it.

> the latest Gen5 NVME drives tend to cap out at ~90MBps for such loads (worst kind of loads)

Possibly scattered 1-byte writes rather than sequential 4096-byte page writes.

Benchmark in English here: https://www.storagereview.com/news/gigabyte-aorus-10000-gen5...

I believe this is battery backed, so it doesn't lose data when powered off. With that said, mmap hard disk file would get similar performance (minus fsync overhead to the persistent disk backing store).

Any idea how this compares to enabling write caching on a drive or on your database layer, if you're using one? I mean other than the catastrophic effects of a sudden power outage.

Reply on news.ycombinator.com