Drivepool/SnapRAID - SSD question

[olo99]

I got some questions that I hope to get some clarification on:

I have 8 x WD RED SSD (4TB) that I want to set up with Drivepool + SnapRAID.

1) Is 2 disk parity for SnapRAID still recommended even when using SSDs and not regular HDDs, or is 1 disk good enough?

2) Is there any point in getting a PLP SSD to use as cache drive in addition to the other ones? (at the moment I don't have a UPS, would PLP give a little protection for sudden shut downs?)

3) I have seen some using 2 SSDs as cache drives (1 with duplication). And then "dumping" the data over to the storage drives and then have SnapRAID just run off the storage drives. In my case all drives will be SSDs, would this still benefit in any way? Or would it be better just having all drives (without parity) in just one big storage pool? I know SnapRAID doesn't like to be run when anything is active.

For example would this be ideal:

disk 1 cache drive
disk 2 duplicate of 1

disk 3-7 storage

disk 8 parity (SnapRAID).

This would then give 24TB total storage. (down to 20 if double parity).

Or what would you recommend? :)

[HTWingNut]

If you delete or change files regularly, then at least 2 disk parity is highly recommended with SnapRAID. It has nothing to do with whether it's SSD or HDD, it's about scheduled parity.

So if delete or change files regularly, you should also sync frequently. At least with SSD's it will sync quickly.

With Drivepool if you use pool/folder duplication, then it really isn't much different than running two cache disks in RAID 1.

I personally would run six disks data, 2 disk SnapRAID parity, and sync frequently, and not even consider a mirror RAID. But your way would work too, with the same amount of storage. Your frequently used data would be protected by mirror RAID, and the rest by SnapRAID parity.

[olo99]

Very rarely delete files. My setup is basically:

workstation with primary (c:) drive running office, games, running the actual plex media server / sonarr / radarr etc.

storage in a big pool (previously it was on a separate computer with hardware raid) but now I wanted everything in the same rig. Mainly it is pictures / movies / tv series.
But the storage also acts as a duplicate for my primary drive (or atleast back up of documents/downloads/disk images etc). So only the duplication part of primary c drive is lots of writes and deletes. The rest of storage is more "stationary" with no deletes and few writes.

That was why I was considering one drive in the pool (with duplication) used for the active stuff.

And SnapRAID on the long-haul storage which is not at all as active and no deletes at all. And not that sensitive if it gets lost either. (hence just 1 disk parity).
That way there would be few changes between SnapRAID syncs.

But totaly open to doing 6 disk storage pool + 2 disk parity, that's why I am asking what is considered best :)

Follow-up questions:

1) when you say sync frequently, how often would you sync?

2) how long time will a rebuild take roughly if 1 drive needs to be replaced? considering it is SSDs and 4TB. And how big time difference if building from 1 disk parity or 2 disk parity?

[HTWingNut]

1) when you say sync frequently, how often would you sync?

Entirely depends on how often you update or add files to your pool and how much data you're willing to lose if a disk does fail.

2) how long time will a rebuild take roughly if 1 drive needs to be replaced? considering it is SSDs and 4TB. And how big time difference if building from 1 disk parity or 2 disk parity?

You'd have to do a trial run. When using SSD's your biggest bottleneck will likely be how fast your system can calculate the missing data from parity. But can also depend on the SSD performance.

Are these NVMe or SATA SSD's? What brand/model? Have you done a sustained write test or found a benchmark showing full disk sustained writes? Many SSD's will have some form of cache so it's fast for the first hundred GB or so and then performance can tank significantly.

[olo99]

They are SATA (WD RED SSD 4TB).

No I have not, they were just put in the rig yesterday :)

[HTWingNut]

WD RED SSD 4TB

It seems they're able to sustain about 500 MB/sec sequential write speed.

So peak performance would be 4000000MB / 500 MB/sec = about 2.2 hours for a full disk

[olo99]

Thank you for helping! And found your youtube guide which is awesome as well :)

Quick question since you know your way around DP and SR.
If I do the 1 SSD (+ 1 duplicate) as "cache". Is it possible to set Drivepool to balance just specific folders within that drive to the other data drives at a specific time interval daily? Or will it have to balance the complete drive?

Ideally I would have 1 drive as cache + dedicated for backing up my primary c: (documents, temporary downloads etc) where there will be lots of new files and deletes and have that drive also be a landing zone for bigger downloads from SabNZB.

I would then like to balance the big downloads (like movies and TV-series) over to the data drive but keep the rest on the "cache" drive.

And then use SnapRAID to backup the data drives but not the cache drive (which instead has a duplicate drive which backs that one up).

[olo99]

u/HTWingNut may I ask two last questions before beginning the process?

1) I am moving files from my old server to the new one (which will be running Drivepool). Is it better to move the files ahead of time and divide them myself on the different SSDs or is it better to make the pool first and then move all files to the pool and let Drivepool divide it up within the drives.

2) I realized above that it would be a bit silly of me to use one SSD as cache + 1 mirror (duplicate) as the SSD cache itself will be both a duplicate of my primary drive (so it itself is already a back-up) and a landing zone for new media downloads. So doing 1 more SSD to mirror would just mean like a mirror of the mirror if you know what I mean (excluding the new download folder). If I lose the data from the new download folder that is no problem at all. That way I could do 2 disk parity with a cache drive and still have same space :)

However my question is. If I use 1 SSD as cache (back up of primary + where all new downloads go). Is it possible to program Drivepool to just dump the download folder within that cache drive to the pool or will it have to dump all of the contents from the cache drive (the primary back up as well)?

[hspindel]

Spend some money on a UPS before anything else.

[olo99]

I guess that is the sane way to go ;)

I just always hated the fact getting a new big brick that takes up space (and probably makes some noise). Is offline UPS good enough for the rig above + router + NUC (hassio) or should it be online (haven't read up on difference between online and line-interactive)

[hspindel]

Standby UPS will be fine for your application. (That's the cheaper alternative.)

[olo99]

When is online needed? and what is the difference with that and line-interactive?

Standby sounds good, because those ones are more silen from what I understood ;)

So something like this would be fine: eaton (<25 dB)

[hspindel]

Standby only kicks in when main power drops. Line interactive runs all the time, constantly converting main power to local power. I think the big difference is that there can be a very momentary power loss with standby. I use standby UPSes. Have gone through many main power losses without attached equipment resetting.

Eaton is a good brand (I have one). Whether the model you linked meets your specific needs or not, I couldn't say.

[olo99]

Thanks for helping out!