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We are planning to get HPE DL380 Gen9 8SFF CTO Servers with HP Smart Array P440ar/2G FIO Controller to setup a MongoDB cluster which will store huge amounts of data. (Assume growing non-stop)

Cluster will have 3 servers initially and will add more servers when needed for sharding.

Each server will have 16 * 10K SAS drives: HPE 1.8TB SAS 10K SFF SC 512e HDD

MongoDB documentation suggests to have storage backed by RAID-10.

It does feel like waste of raw space considering RAID-10 yields only %50 usable size.

RAID-50 will give remarkably more storage, but only one drive can fail per sub-array, in case of re-build, performance degradation can be bad.

RAID-60 will use an additional disk for parity per sub-array, will have less performance, less space but more resilient.

My options with 16 * 1.8TB disks, using this calculator:

RAID-10: 13.1 TB
RAID-50: 22.9 TB
RAID-60: 19.6 TB

I've never dealt with an array of this size, considering challenges for a volume this large:

  • RAID-60 costs additional disks but is performance penalty considerably less during degradation/rebuild?
  • Any other pros/cons I should consider?
  • R5/50 has no place in 2017, especially with large 'spinny' disks. – Chopper3 May 27 '17 at 7:49
  • They're not large disks... enterprise SAS 10k. R50 and even R5 is okay. – ewwhite May 27 '17 at 7:49
  • @ewwhite by 'large' are we talking about physical component size? – sdkks May 27 '17 at 8:19
  • @Chopper3 can you elaborate more on cons in an answer? – sdkks May 27 '17 at 8:19
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Sure. It's fine.

  • What are your actual I/O requirements?
  • How much space do you need?

(those should be driving the decision making process, not the idea of perceived waste)

Granted, you can test with your own data, but these days, you're talking about 12G Smart Array controllers on modern high-end hardware, 2GB of write cache and plenty of spindles. It'll be fine whatever you do. R6 with spares, R60, R50, with spares, etc.

Rebuild performance is not bad on HP servers; especially with enterprise SAS drives.

But I'll add that SSD pricing has come down significantly. Are they an option here?


Edit:
Be careful with the config here. You listed an 8-bay model, so a SAS expander will be involved.
There are 24-bay models of the server in question available. I don't know if that helps your planning.

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  • Space I get with RAID-10 is fine, it's about %20 more than our projected use. That being said, it doesn't give me too much comfort knowing we could have a lot more with RAID-50/60 and have zero risk of having to invest for more storage prematurely. SSD for my locality is too expensive, could only add couple of them for lvm caching perhaps. – sdkks May 27 '17 at 8:16

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