RAMdisk slower than disk?

user_227567 0
Viewed 8045

A python program I created is IO bounded. The majority of the time (over 90%) is spent in a single loop which repeats ~10,000 times. In this loop, ~100KB data is generated and written to a temporary file; it is then read back out by another program and statistics about that data collected. This is the only way to pass data into the second program.

Due to this being the main bottleneck, I thought that moving the location of the temporary file from my main HDD to a (~40MB) RAMdisk (inside of over 2GB of free RAM) would greatly increase the IO speed for this file and so reduce the run-time. However, I obtained the following results (each averaged over 20 runs):

  • Test data 1: Without RAMdisk - 72.7s, With RAMdisk - 78.6s
  • Test data 2: Without RAMdisk - 223.0s, With RAMdisk - 235.1s

It would appear that the RAMdisk is slower that my HDD.

What could be causing this?

Are there any other alternative to using a RAMdisk in order to get faster file IO?

ramdisk file performance
6 Answers

I join the people having problems with RAM disk speeds (only on Windows).

The SSD i have can write 30 GiB (in one big block, dump a 30GiB RAM ARRAY) with a speed of 550 MiB/s (arround 56 seconds to write 30 GiB) ... this is if the write is asked in one source code sentence.

The RAM Disk (imDisk) i have can write 30 GiB write (in one big block, dump a 30GiB RAM ARRAY) with a speed of a bit less than 100 MiB/s (arround 5 minutes and 13 seconds to write 30 GiB) ... this is if the write is asked in one source code sentence.

I had also done another RAM test: from source code do a sequential direct write (one byte per source code loop pass) to a 30GiB RAM ARRAY (i have 64GiB of RAM) and i get a speed of near 1.3GiB/s (1298 MiB per second).

Why on the hell (on Windows) RAM Disk is so slow for one BIG secuential write?

Of course that low write speed happens on RAM disks on Windows, since i tested the same 'concept' on Linux with Linux native ram disk and Linux ram disk can write at near one gigabyte per second.

Please note that i had also tested SoftPerfect and other RAM disks on Windows, RAM Disk speeds are near the same, can not write at more than one hundred megabytes per second.

Actual Windows tested: 10 & 11 (on both HOME & PRO, on 64 bits), RAM Disk format (exFAT & NTFS); since RAM disk speed was too slow i was trying to find one Windows version where RAM disk speed be normal, but found no one. Actual Linux Kernel tested: Only 5.15.11, since Linux native RAM disk speed was normal i do not test on any other kernel.

Hope this help other people, since knowledge is the base to solve a problem.

user_177546660
Related