New build. RAID5 on RST ok?

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rajdude
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Re: New build. RAID5 on RST ok?

Post by rajdude » Fri Mar 15, 2019 2:26 am

Hmmmm........I like the drive pooling idea. Allows me to use existing, old disks which are still usable.

But how can I use Stablebit Drivepool + SnapRAID in the same array and system

Drivepool will try to pool different capacity disks. But doesn't snapRAID need identical disks in the array?

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Jaga
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Re: New build. RAID5 on RST ok?

Post by Jaga » Fri Mar 15, 2019 3:21 am

rajdude wrote:
Fri Mar 15, 2019 2:26 am
Drivepool will try to pool different capacity disks. But doesn't snapRAID need identical disks in the array?
Neither software needs identically sized data drives. The only limitation is that your parity drive(s) need to be as large as the largest data drive in your pool. So if you're doing a single-parity SnapRAID solution, your largest single drive should be your parity drive. Drivepool really doesn't care at all what you use for data drives, and it has flexible balancers.

rajdude
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Re: New build. RAID5 on RST ok?

Post by rajdude » Mon Mar 18, 2019 5:35 pm

The more I read about snapRAID the more I worry about it. The main issue is that the parity is not calculated when files are written to the disk.

My typical use case: Usually, I just copy the contents of my camera memory card to the server and it is all good. RAID5 calculates parity and writes parity in real time, (while the photos were being copied to the array).

SnapRAID does not do that. It will calculate and write parity the next time that job is scheduled. That gives me a HUGE heartburn. There is a possibility that the files from my memory card were not written correctly to the disks and I would not know until snapRAID tries to read and calculate parity next. By that time, I may have formatted and re-used my memory card in the camera.

This issue has been highlighted here by a blogger:
https://blog.joefallon.net/2017/07/warn ... aid-users/

Then there is the other issue: slow read write performance.
With a proper hardware based RAID array, the more disks you add to the array, the faster disk I/O happens. With snapRAID you get whatever disk I/O you get from one single disk. This worries me a lot; because these days these high capacity disks (NAS or not) are all very slow 5400 rpm drives. And 7400 rpm drives are significantly expensive in comparison.

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Jaga
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Re: New build. RAID5 on RST ok?

Post by Jaga » Tue Mar 19, 2019 2:22 am

And yet - the security and robustness of a non-RAID drive pool far surpasses any RAID solution. Here's a bit of reading for you on it:

Why RAID 5 stops working in 2009

Why RAID 6 stops working in 2019

If you setup a simple script every X hours (or nightly, weekly, whatever you want), you can update your SnapRAID parity when you choose.

Add to that the flexibility of adding any drive to a pool (any size drive of any type - HDD, SSD, USB, etc) on-the-fly, balancing what files you want wherever you want, and so on... and I don't see much of a reason to do RAID anymore. It just has too many failing points the larger disks you give it. I honestly would feel nervous about setting up a new RAID array for any kind of data now. The slightest hiccup from the array (needing to re-verify a drive) and you risk losing the entire array.

As for speed - you can get around that if you want by setting up pool mirroring on member drives that are RAID 0 targets. i.e. two drives are setup in RAID 0 and the resulting volume is presented to the Pool as a target. Another 2 drives of identical size are also RAID 0'd and presented as another target volume. Then you mirror using the Pool so that data that lands on one target, is duplicated to the other. And you have much faster speeds for reading and writing, not to mention redundancy on the two volumes in case any one of the four drives dies.

neatchee
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Re: New build. RAID5 on RST ok?

Post by neatchee » Mon Mar 25, 2019 9:36 pm

A coworker with a lot of experience and interest in this area pointed me towards the following document as the "way forward" in terms of durable storage to replace traditional RAID.

https://access.redhat.com/documentation ... code_pools

Erasure Code Pools is apparently where professionals working in this area are headed, since RAM and CPU resources have become more abundant.

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Jaga
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Re: New build. RAID5 on RST ok?

Post by Jaga » Tue Mar 26, 2019 7:51 am

Sounds interesting, but not available for any version of Windows from what I could tell. Storage spaces has some type of erasure coding built in, but it's not nearly as robust as something like Drivepool. I tried Storage Spaces for about 9 months, then swore it off.

neatchee
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Re: New build. RAID5 on RST ok?

Post by neatchee » Wed Mar 27, 2019 8:55 am

Yes, from what I understand most implementations of erasure coding are designed for big-data and business environments; multi-node setups rather than just multi-disk.

As the limitations of RAID6 become more real for consumers maybe we'll see more action in this area for home users.

In the meantime I'm just sticking with RAID10 for it's simplicity. Spinners are cheap these days anyway.

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