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These are used in servers and NAS devices. But why would it really be necessary?

  • Is it mostly to offload the RAID management and calculations to a different CPU than the one from the machine? Or does that matter more for a server that has many more tasks than a NAS?
  • Aren't the SATA (or SAS if there exist any) ports on the motherboard sufficient if it covers the number of drivers you need? They each work at at least 6 Gb speed for SATAIII? And the load on the CPU for RAID calculations probably is not that high?
  • I know that one with a cache and battery increases storage reliability in the case of power losses. But don't a UPS for a server/NAS already cover that field?
  • Using BTRFS or ZFS for storage reliability in a RAID environment, would this make the controller card quite useless except for being able to have more ports and offloading RAID activity?
aardbol
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1 Answers1

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Is it mostly to offload the RAID management and calculations to a different CPU than the one from the machine?

If you have a HW RAID controller: Maybe. This gets less important with ever faster systems where RAID calculations don't have a noticeable impact anymore.

Aren't the SATA (or SAS if there exist any) ports on the motherboard sufficient if it covers the number of drivers you need?

What if not?

I know that one with a cache and battery increases storage reliability in the case of power losses. But don't a UPS for a server/NAS already cover that field?

What if your system PSU fails? What if the outage last longer then your UPS can handle? Modern caches are often flash backed and can last years if necessary.

Using BTRFS or ZFS for storage reliability in a RAID environment, would this make the controller card quite useless except for being able to have more ports and offloading RAID activity?

If you can use a modern FS like this (and that's a big if), you might not want to use HW RAID, but non-RAID controllers exist and you often can turn off RAID anyway. Still, they offer more ports (and SAS capability if the board don't offer this).

In short: You will know if you need an external controller.

Sven
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