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fmp4m

Advice on Build (r420 rack server - all SSD)

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I am rebuilding a R420 server, with all SSD drives.  (8 x 1TB SSD).

 

My question is,  what would be the optimal configuration, given it will be speedy (primary use is high-speed data needs on a 10GbE network).

 

7x Data 1x Parity and no Cache?

6x Data 1x Parity and 1x Cache?

5x Data 2x Parity and 1x Cache?

5x Data 1x Parity and 2x Cache?

 

I have been weighing this and can't come to a conclusion.   Please lend your advice and reasoning here?

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What model SSDs and what performance are you expecting? Note that array devices can't be trimmed and parity should be a faster device than the others, since it will be overworked, for example I use an NVMe device for parity.

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Samsung 860 EVO 1TB SSD 3-bit MLC V-NAND SATA III 6Gb/s

 

No room for an NVME in this rack server.   Ultimately,  I am looking for consistent speed that is reliable for rapid-access data.   The speed is from the read part of the server that I need,  not the write.

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11 minutes ago, fmp4m said:

The speed is from the read part of the server that I need,  not the write.

In that case I would go with 7 data + parity, ideally use the latest beta since it has a new alignment for SSDs that is better for performance and endurance, you should get at least 300MB/s reads for large files, possibly more.

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Is there a different SSD you would recommend,  or in your opinion, would I be better going a different route than full SSD?  

Im open to full suggestions and value your opinion JorgeB

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860 EVO one of the best SATA SSDs you can get, jut make sure to use the latest beta since Samsung SSDs appear to be sensitive to partition alignment. 

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On 9/11/2020 at 12:28 PM, JorgeB said:

... and parity should be a faster device than the others, since it will be overworked, for example I use an NVMe device for parity.

A question, please ... [I might be missing something, since I don't use Unraid.] :

For an all-SSD array, wouldn't turbo-mode alleviate the parity-dominating aspect (with no detrimental side-effects)?

["good" SSDs (sata), and in decent "trim", will get write speeds very close to their read speeds, no?]

 

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13 hours ago, UhClem said:

For an all-SSD array, wouldn't turbo-mode alleviate the parity-dominating aspect (with no detrimental side-effects)?

Turbo write helps with speed, parity will still be overused compared to data devices, if for example you have 10 data devices, over time parity will have 10 times the number of writes of any data device, so you want a device with better endurance and since it can't be trimmed and will be much more used faster performance will also help.

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10 hours ago, JorgeB said:

... so you want a device with better endurance and since it can't be trimmed and will be much more used faster performance will also help.

Thanks!  Good points.

I think that spec'd endurance (e.g., 600 TBW for 860 EVO 1TB) won't be an issue, for all but extreme use cases. (For a data point, I used a 860 EVO 500GB in a DVR (DirecTV HR24) for the last year. It had ~8000 hours and ~30 TBW when I secure-erased it. Sadly, I didn't think to do any write-performance tests before the erase.) An "extreme use case" might be an array for multi HD security cameras [e.g. 4 feeds @ 10GB/hr each (24/7) =~ 350 TBW/year]. Note, though, that you need a near-server-level NVME to exceed 1 PBW rating (for 1 TB device).

 

As you said, the NVME-for-parity does offer significant performance "head-room", such that it's write speed can degrade (as expected w/o trim) with no effect on array write speed. It also allows one to forego turbo mode, eliminating read-contention with the other (N-1) data SSDs [during array writes] ... and a few watts of juice.

 

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Revisiting this, as recent fluke timing - my motherboard lost died (PCIe + Sata channels died).   I have to replace my main server - which is all SAS/SATA drives.  I had stuck in my head NVME for cache not Parity - so I ordered a server grade mobo with two m.2 slots to put those in per this threads recommendations.

 

Well, I come back to review and realize you said parity.   If I have 8tb drives in my array, I would need 8tb parity drives.  How the hell would one do that? The cheapest quality 8tb nvme is the Sabrent Rocket ($1400) and I would need two to protect my 27 drive (soon to grow to add more drives to fit in my 42 bay chassis).  That would be $2400 in parity alone.

 

I am reading you right that you recommend / use NVMe for Parity right?   What size parity do you have?

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Parity just needs to be the same size as the largest data device, you were talking about 1TB SSDs for data, so you only need a 1TB SSD for parity, and yes, a fast NVMe device with good endurance would be better.

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Hi JorgeB

 

That makes perfect sense for the 1tb build.  I was trying to utilize the same knowledge in picking hardware for repairing my main rig, when I realized it was unfeasible to do.

 

Sorry for any confusion.  In my main rig, would you still advise a 8tb nvme or would 8tb 10k/15k sas be plenty?

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Not much point on using flash parity for HDD array, unless you plan on writing to multiple disks at the same time.

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