I have an Unraid setup with

• 1 array with 2 x 12 TB disks (one parity)

I will be migrating soon all my TV Series / Movies / Music... from a Synology NAS where the data is stored on 2 x 20 TB disks in RAID 1.

Lets say I would have 3 x 20TB drives to put on my Unraid for this and would like to have the capability to expand it, how would you recommend to set it up?

• creating a Pool or adding them to my array? (if I add them to the array I would have to change and rebuild the parity drive I suppose)

• how to setup some kind of RAID 3 or 4?

• is there some flexibility in terms of drive size?

Array is more flexible for expansion, e.g., you can use different sized drives, with 7.2 you can also expand a RAIDZ pool; the drive would need to be the same size, or larger, but it wouldn't use the extra space.

The array is more flexible; the pool is faster. I would choose according to your priorities.

Thank you for your recommendation. So the best would be to use the Array. From my understanding the main inconvenient of using the array is that it is slow for writing, right?

• knowing that I would keep writing (torrent), is that low writing speed acceptable?

• it would be ok for reading though I guess?

• and for such setup, do you think one parity drive is enough? data is not critical as it can always be downloaded again

The array is more flexible; the pool is faster. I would choose according to your priorities.

Flexibility is great, as long as speed is sufficient.

13 hours ago, Vorko76 said:

From my understanding the main inconvenient of using the array is that it is slow for writing, right?

Writing and reading, the array drives are separate filesystems; they are not stripped, so the max read speed is that disk's speed at that position.

Write speed with normal write mode will be considerably slower than that, typically 40-60MB/s, with turbo write enabled, it will be as fast as the slowest disk at that position, assuming no controller bottlenecks.

What JorgeB writes is correct (He almost always is). But for torrent, there is other things to consider, as everyone has different work loads, depending on what they are doing:

• How many files will be active at one time?

• How much data (total storage size) will be actively downloading/seeding?

• How fast is your up/down WAN speed?

• Are the files you are torrenting recent/popular, that there will be many requests for them?

I no longer torrent, but I did in the past. It can put quite the burden on your system, depending on the answers above. Many files, actively seeding, and a fast pipe will have a lot of disk activity. As files tend to be more fragmented on the drive (due to being written in segments as downloaded), spinning array drives will be thrashing around when reading data to upload.

If you are planning on a lot of torrent activity (or seeding for a period of time) it may be best to have the torrent files on a dedicated pool SSD (or NVMe) while they are actively seeding, then moving them to your array once they are completed (and you no longer wish to seed). This prevent the spinning drives in your array from being busy all the time while active torrents exist. It also will defragment the files when copied from the SSD to the array.

Most torrent clients have some sort of function for managing the movement from the "download" drive to the final drive location.

Edited August 31, 2025Aug 31 by ConnerVT

19 hours ago, Vorko76 said:

and for such setup, do you think one parity drive is enough? d

The choice of one vs two parity drives is a difficult one.

If you do regular parity checks to make sure that your hard disk are healthy, you can look at this thread for some thoughts of single vs dual parity using a statistical approach:

https://forums.unraid.net/topic/50504-dual-or-single-parity-its-your-choice/

There also a school of thought that looks at dual parity as 'belt and suspenders' approach to data recovery. You can read about that school here:

https://forums.unraid.net/topic/50504-dual-or-single-parity-its-your-choice/#findComment-552912

In the end, it all comes down to your comfort level is in dealing with risks to your data. You are the only one who can make that choice in the final analysis.

And remember that disk failure is not the only way to lose your data. Think of fire, flooding, lightening, theft of equipment, vandalism, malware to name a few.

Thanks for everything, everyone. Thats clearer

On the parity topic, I personally run dual parity (I added a second parity drive as soon as the feature was available). I like that if I have a drive failure, the extra parity protects my data while I replace the failed disk. All if the data on my array is also "replaceable", but my time has value and if paying for an extra drive keeps me from having to spend the time to rebuild everything, then it's very cheap insurance. If you lose data (especially 10s of terrabytes), just figuring out what you lost can be a tall order. A few hundred bucks for an extra drive will seem very cheap at that point.

Speaking of failure, another array feature that I don't think was mentioned is that because unraid uses dedicated parity and the individual drives just contain standard filesystems, if you lose a data drive (and don't have parity to rebuild it) then you lose ONLY what was on that one drive since the data isn't stripped. On a conventional stripped array you would lose everything.

43 minutes ago, WizADSL said:

Speaking of failure, another array feature that I don't think was mentioned is that because unraid uses dedicated parity and the individual drives just contain standard filesystems, if you lose a data drive (and don't have parity to rebuild it) then you lose ONLY what was on that one drive since the data isn't stripped. On a conventional stripped array you would lose everything.

Yes I had read that. That's quite a game changer compared to Synology JBOD.

But thank you for your advice.