0

Let's say I have a dual CPU system with:

  • 2 x Intel Xeon E5-2667 v4 3.20GHz 25MB Cache
  • 3 x 1TB SATA3 Seagate Enterprise class in RAID5 on the Intel C612 RSTe Controller
    • Total final storage is: 2TB
    • Fault tolerance: 1
  • 256GB RAM

The Intel RSTe is also informally known as fake RAID. So the RAID processes are done at the firmware level, but still by the CPU using the RAM of the machine.

This server will hopefully run the CPU at close to 100% almost always and the RAM will also be almost capped, almost always.

At some point, obviously, one of the drives in the RAID will fail and it will be replaced and the RAID array will be rebuilt.

In this scenario, will the rebuild take a very limited CPU amount, maybe 1%, and also minimum RAM, maybe a few GB, so the overall impact on the processing will be minimum? Or will it take 20% (or more) CPU, which means that whatever I am doing it will take 25% more ?

Andrei
  • 101
  • Don't use FakeRAID and don't use RAID5. You are much better off using the software RAID (6/10) implementation of your OS of choice. – Sven Oct 14 '16 at 15:19
  • The effect on CPU isn't that big. The biggest effect is on I/O performance. – Tero Kilkanen Oct 14 '16 at 15:42
  • @Sven Why? I could maybe also switch to hardware raid also, but it is more expensive and I don't know if it is worth it for my particular application. Is software RAID 6/10 always better than fakeRAID5 for any application under any circumstances? – Andrei Oct 14 '16 at 16:12
  • @TeroKilkanen Not that big, but how big? I want to be able to give accurate estimates when I'm saying I will deliver something in 5 weeks. Will it be 5.5 weeks, will it be 6 weeks? Do you have any experience or second hand experience or documentation with a similar system that needed a rebuild? – Andrei Oct 14 '16 at 16:15
  • @Andrei: FakeRAID has a terrible reputation as being really unreliable without any real benefit to it (after all, the CPU/RAM is involved anyway). Also, you tie yourself to that specific hardware model and can't just move the controller with you if you need to switch to other hardware for whatever reason (software RAID is portable by definition). RAID5: See the discussion about UREs in the RAID5 part [here](http://serverfault.com/questions/339128/what-are-the-different-widely-used-raid-levels-and-when-should-i-consider-them) - it's just too risky in my view (even for smaller arrays). – Sven Oct 14 '16 at 16:25
  • Also, regarding rebuild rates: With a RAID5 you are 100% exposed to another disk failure during rebuild and in most cases, I would want to keep the exposed time as short as possible, even to the detriment of production use. And, speaking for Linux software RAID, you can easily control the sync rate if necessary. – Sven Oct 14 '16 at 16:35
  • @Sven One of the advantages of fake RAID is that you can install the OS on them. Also, some suggest that they might be marginally faster. Everything on the hddrives is not meant to stay for longer than needed, so the purpose of RAID is not to safe the data for long time, but to make sure that the data is available for the 1 to 6 weeks necessary for the process running on the unit to finish. Then everything is moved and new data comes in. – Andrei Oct 17 '16 at 13:09
  • Well, suit yourself. – Sven Oct 17 '16 at 13:11

0 Answers0