Home / server / Questions / 993848
Accepted
Ole Tange
Asked: 2019-12-01 05:30:34 +0800 CST

Mixing DIMMs in Dell R815

  • 772

I am about to upgrade RAM of a Dell R815 with 4 AMD 6174. Current working config is 8 x 16GB RAM (2 on each CPU) of unknown specs. I will be adding 24 x 16GB 4Rx4 PC3L-8500R-07-10-F0-D2 M393B2K70CM0-YF8 1129

I have heard rumors that mixing RDIMMs from different suppliers may cause stability issues - even if they are compatible on paper. Is there any documentation of that?

If so: Can I mitigate this by moving the existing 8 RDIMMs to a single CPU and putting the 24 new on the remaining CPUs?

memory

1 Answers

  1. Best Answer

    The old ones were 2Rx8, thus of a different rank. The manual of R815 specifies that you can mix different ranks, but that the higher ranks must be put before the lower ranks.

    So I had to mix the different suppliers: Socket A-D1-6 contains the new DIMMs, and socket A-D7-8 the old DIMMs.

    Mixing them in a different order causes the server to flag multiple DIMMs as faulty. In other words: Following my idea of putting all the old DIMMs on a single CPU did not work.

    Stability seems to be OK: After one night of Memtest86 zero errors were found.

    A peculiar find is that mixing the 1600 MHz DIMMs with 1066 MHz DIMMs causes all to be clocked at 800 MHz. In other words: The 1600 MHz DIMMs do not support running at 1066 MHz, so if RAM performance matters more than RAM size, removing the old 1600 MHz DIMMs completely would give a faster RAM speed.

    • 1