Mix Raid? bay arrangement for raid 10? different raids performance benchmarks?


I hope that I’m not only helping myself by these questions but also helping others who didn’t find answers to such questions…

Before we start, let’s agree on few points. I read a lot about all raid options Raid-0, Raid-1 , Raid-0+1, Raid-10(1+0), Raid-5, Raid-6, Raid-50, Raid-51, Raid-60, and Raid-61. So the questions here are not about principles of these RAIDs work, I think there are a lot of reference for all of them.

My questions are specific to WD PR4100 and how does it apply the previously mentioned principles (practically):

1- In the 40TB pre-configured, what are the drives installed? RED or RED-PRO? cash? RPM? transfer rate?

2- In RAID-10, what is the drive bay arrangement? (1=2 + 3=4) or (1=3 + 2=4) or (1+2 = 3+4)
In other words:
[Option 1]: If I lost disk 1 I can rebuild from disk 2 (and vise versa), and if I lost disk 3 I can rebuild from disk 4 (and vise versa)
[Option 2]: If I lost disk 1 I can rebuild from disk 3 (and vise versa), and if I lost disk 2 I can rebuild from disk 4 (and vise versa)
[Option 3]: If I lost bay 1 and 2 (both), will I be able to rebuild my data from 3+4?
(This can help the use of 2 different types of HDD (EX. WD-Ultrastar & WD-Red) and try avoiding having a similar life span which can can affect the recovery process when all HDDs age together)

3- In RAID-10, does the read happen from one of the sides only? (one raid-0 side)
(If that is the case, Using WD purple can help saving on cost and add more durability/heavy duty for a continuous writing on the side which is writing and not usually used for reading)

4- Can I setup 3 drives to be working on raid-0 or raid-5, and keep one as a JBOD and make a scheduled daily backup of my critical data (folder/share) from the Raid-0 to the JBOD?

5- RAID-5 redundancy is a great balance between space & data safety and it makes sense why you set it as default but I’m concerned about the compression speed for the parity section and how far does it affect the write speed on the PR4100 (will the user still feel the speed difference even with the Pentium quad-core CPU and after an upgraded RAM to 16GB on the PR4100?)
In other words, Is there any comparison chart/benchmark for read & write speeds for JBOD (Control), Raid-5, Raid-10, and Raid-0 on PR4100 specific? (want to know how much speed is sacrificed for the extra storage to help decide between RAID-5 & RAID-10 or even Raid-0 with External backup)

6- I have multiple “my passport 4TB” USB drives, and I read that PR4100 can backup to USB drives but I have 2 questions.
A- How will it interact with password protected “My passport” (will it ask for password? can I save the password so It will automatically unlock for the scheduled backups in the future?)
B- As I have mentioned, I have multiple WD MY passport, will the PR4100 be able to differentiate between them for different backup activities for each? (Ex. 1 drive is to backup My document while the other is to backup family photos, a 3rd one for Media, and a 4th for work projects)?

7- Last question, on Youtube, one review said that PR4100 did not detect a faulty drive and kept running in Raid-1 mode without warning the used about the bad drive. This is very critical because if a user didn’t know that he/she lost one drive, the situation will be disastrous when the second fails and all the data get lost with no way to recover. Was this issue resolved? what types of warning does PR4100 generates (buzzing/beeping/LED/software pop-up)?

I know that my questions are so specific and geeky a bit but I want to make a knowledgeable decision and help others do the same so they know what to expect for their money.

I’m not expecting answers for all the questions from one person, but you can share your experience or knowledge about any of the points above.

Thank you all in advance for your kind support.

Best regards,
A Georgy

Hi AmgAdly,

WD My Cloud PR4100 supports RAID 0, RAID 1, RAID 5, RAID 10, JBOD and Spanning. Answers to your questions are:

1- In the 40TB pre-configured My Cloud PR4100 you will find four 10 TB WD Red drives inside with the following specifications:

Cache: 256 MB
RPM: 5400
Interface: SATA 6 Gb/s

2- In RAID 10, the drive bay arrangement is (1=2 + 3=4). Option 1 as per your query is correct.

3- In RAID-10, read operation will take place on one side only i.e. drive 1 and 3 but you can’t use any other drive in this arrangement as this can affect the RAID. It is always recommended to use the same drives for RAID arrangements such as RAID 10.

4- Yes, you can setup 3 drives as RAID 0 or RAID 5 and 1 drive for JBOD but you won’t be able to backup the data from RAID 0 or 5 to JBOD drive as the JBOD drive will have less capacity than the other RAID. It is always recommended to use a drive for backup with at least twice the capacity as compared to the source drive.

5- RAID 5 would stripe data and parity across three or more disks. In this RAID set, if a drive would fail, the data is automatically recreated from the parity and distributed data once the new drive is installed. This RAID set is the most common for business servers and NAS devices. It will have good read performance, but will have a hit performance on write speeds since the parity data needs to be recalculated with new data written on the drive. The size of about one of the drives will be lost in the RAID set in RAID 5. However, there’s no fixed benchmark present. To know more refer to the link below:


A- You won’t be able to backup the data to password protected My Passport drives. The drive needs to be unlocked while taking the USB backup.

B- Yes, My cloud PR4100 can differentiate between different My passport drives. Make sure you create the USB backup as incremental backup.

7- My cloud PR4100 device has dedicated drive LED indicators that turns red when there’s something wrong with the drive and also you will receive a notification on the user interface of the device as well regarding the same.

I hope this answers most of your questions.


Hi Professor_X,

Thank you so much for spending the time and effort to answer my previous questions.

It would be great if can have a look at the below link and tell us the reason for failing test1 in the article:

Was any action (firmware) taken to cover the above mentioned bad HDD detection failure?

I read a lot about Raid arrays and came across ZFS which seems to me a safer option as it covers the silent data corruption by providing data checksum to avoid any raid loophole which I have personally experienced before where the drive might look healthy and has no issues but the data is getting corrupted.
So, does PR4100 has a native ZFS solution?
I also saw this article in the forum: " [FIRMWARE] FreeNAS on PR2100/PR4100 - updated! " which is showing a great capability to use FreeNAS on PR4100. Would this be the only way to enable ZFS/Raid-Z on the device?

WD can’t ship zfs in its firmware due to licensing. Same reason why its not found in synology devices. Only when you install other firmware such as debian, freenas or ubuntu you can have zfs.