Okay, just set this thing up, updated the firmware, etc.
Disks are:
3tb 3tb 2tb 2tb 2tb 2tb
It is set up as Raid Level X-Raid2 6 disks. But for some reason the volumes of the 3tb drives show up as 2, despite it acknowledging that they are 3tb disks.
Are there any practical negatives to installing mixed size disks like this into the Pro 6?
If you have an existing array with empty slots, then you can only fill the empty slots with the largest installed size (or larger). Similarly, replacement disks either match their existing size, or are the largest size (or larger).
Dual Redundancy requires 4 drives of the largest size.
Forensic recovery might be harder, as the volume is built up of multiple RAID layers.
I've run a mix of 1.5 TB and 3 TB in my Pro 6 for a while now, with no issues. Currently it is 2x1.5 TB + 4x3TB.
Note for your setup your 3 TB will be useless until you get another 3 TB drive because of the dual redundancy (XRAID6) you need 3 disks of each drive size to live up to the statement "dual redundancy" In your current setup you have 3,3,2,2,2,2. If you lose a 2 TB disk your okay another, 2 TB drive will cover it. If you lose a 3 TB drive disk nothing can cover it and live up to the statement that you have dual redundancy in the case that you lose any disk. Get another disk of 3 TB in size or replace (vertical expand) one of your 2 TB drive with another 3 TB drive. Im not sure if you have another slot for an extra disk so verticle expansion is possibly all you have left to deal with. There is nothing wrong with your NAS its reacting the way it was designed to react to minimize damage to data and to increase reliability.
Single Disk Redundancy Disk Space with Raid 5 [base 10]: 11000.000 GB = 11.000 TB Final Useable/Filesystem Size with Raid 5 [base 2]: 10172.736 GB = 10.093 TB
Dual Disk Redundancy Disk Space with Raid 6 [base 10]: 8000.000 GB = 8.000 TB Final Useable/Filesystem Size with Raid 6 [base 2] : 7391.003 GB = 7.333 TB
Negative I believe that is not correct mdmg - in the over all process you would be correct, but in expansion that is incorrect. To get RAID 6 you need at least 4 drives, but to get mdadm to let you get another md after your md2 with RAID 6 you only need 3 disks.
You see Im talking about the extra MD that was created with the oversized disks (md3). You can create a RAID 6 out of 3 block devices....Here is my proof... how many disks are needed for RAID5? 3 right... well then why does our NAS expand the md3 after 2 disks. Look at logs for a setup of 2,2,2,3,3 with RAID 5 you will see that the md3 is expanded with only 2 block devices (the last two 1 TB big portions [2tb to 3tb] of the 3 TB drives are used). Here is a visual of it on readynas.com : http://www.readynas.com/?cat=53 Note that after the 2nd disk upgrade the Volume gets upgraded... Meaning that md3 expanded and is adding its space to the LV /dev/c/c.
However in this case I dont know if the 3 tb drives were put in first or last. If they were put in first he needs to back up all his data to remote place and then factory default the nas with the 3,3,2,2,2 setup and then upgrade one of the disks to 3tb. If however the 3TB drives were put in last then the user just needs to add another disk to experience volume growth.
The best resolution for the issue is for the user to include the logs - please provide us a link to your zipped up logs (System-Status-Logs-Download All Logs). The user can put them in Dropbox public folder or any internet file sharing service and just provide us the link.
In other words - its hard to put this into words people can visual
To start raid 5 you need 3 disks but to expand raid 5 you only need 2 - with mdadm software To start raid 6 you need 4 disks but to expand raid 6 you only need 3 - with mdadm software
You see Im talking about the extra MD that was created with the oversized disks (md3). You can create a RAID 6 out of 3 block devices....Here is my proof... how many disks are needed for RAID5? 3 right... well then why does our NAS expand the md3 after 2 disks. Look at logs for a setup of 2,2,2,3,3 with RAID 5 you will see that the md3 is expanded with only 2 block devices (the last two 1 TB big portions [2tb to 3tb] of the 3 TB drives are used). Here is a visual of it on readynas.com : http://www.readynas.com/?cat=53 Note that after the 2nd disk upgrade the Volume gets upgraded... Meaning that md3 expanded and is adding its space to the LV /dev/c/c.
That animation is for X-RAID2 single-redundancy.
kossboss wrote:
In other words - its hard to put this into words people can visual
To start raid 5 you need 3 disks but to expand raid 5 you only need 2 - with mdadm software To start raid 6 you need 4 disks but to expand raid 6 you only need 3 - with mdadm software
The thing is though in the first case you have single-redundancy. Say a RAID-5 layer of 6x2TB + RAID-1 (that could be converted to RAID-5 when more disks are added) of 2x1TB.
In the second case whilst you could do e.g. RAID-6 layer of 6x2TB + RAID-5 of 3x1TB that wouldn't be dual-redundancy any more, so four disks are required for the volume to expand (regardless of when new md devices are created). When you add a third 3TB disk it might create a degraded RAID-6 layer but in order to maintain dual-redundancy it wouldn't be able to make use of it to expand the volume till a fourth disk is added.
I recently expanded my Ultra 6 volume. I had 6x1.5TB disks installed and I'm using X-RAID2 dual-redundancy. I had to install 4x3TB drives before expansion took place.
2x3tb + 4x2tb was zeeboid's setup, not kevikev's. Kevikev was asking generally about drawbacks of mixed size arrays, he didn't specify any specific config.
In principle you can get dual redundancy with 3 drives (simply by extending RAID-1 to a triple mirror). It would not be normal RAID-6, but it would be dual redundancy. However, my understanding is similar to mdgm's. While it may be theoretically possible, XRAID-2 won't do it.
I recently expanded my Ultra 6 volume. I had 6x1.5TB disks installed and I'm using X-RAID2 dual-redundancy. I had to install 4x3TB drives before expansion took place.
Thats an initial setup where you need the 4 disks to start RAID 6 with mdadm software. However this doesnt cover the expansion topic where you only need 3.
You will need to look at his logs when he adds a 3tb drive.
Md3 will be raid 6 with [UUU] - The raw disk space will be 1 TB extra
Each X represent 1 TB of raw disk space
XX XXXXX XXXXX
Currently here is what is going on (from here on out each X represents 1 TB of raw disk space and each O represents 1 TB of redundant space)
OO OOXXXX OOXXXX
[Raw disk space used (not including overhead and not including kilo to kibi conversions): 8TB and redundancy space will be: 3 TB]
The second he adds a third drive it will work
OOX OOXXXXX OOXXXXX
[Raw disk space used (not including overhead and not including kilo to kibi conversions): 11TB and redundancy space will be: 6 TB]
Although just having three 3TB disks will not give you RAID 6.
However in the setup of going from 3,3,2,2,2,2 to 3,3,3,2,2,2 I believe it will mdadm "cat /proc/mdstat" will say raid 6 and it will show you [UUU] and the extra TB will be used
Any how What it comes down to is this Add another 3 TB drive or add 2 more 3 TB drive. Lets see when it actually expands the volume using some of the extra md3 space (the extra space from the 3tb drives)
##############
I understand that if you start for example with
two disks X tb each and then add another X tb drive then it can be RAID 5 and then add another X tb disk it can become RAID 6.
Then if you add 3 disks of Y size. Y being X+a. You will be able to see the +a being used for volume after the 3rd disk
NOTE: () Parenthesis around the Redundancy
================================
(Y)XXXX raid 6
[Equals]
(a) (X)XXXX
all the X portions make md2, the extra "a" from the Y disk makes md3, Ys extra "a" is wasted
================================
Same with the next setup
(YY)XXXX raid 6, both Ys extra double a are wasted
(aa) (XX)XXXX
Both those "a" make the md3 but they cant be "raid6"ed yet by mdadm so its useless - in a way
================================
With next add ition mdadm will allow the dual redundancy to work
(aa)a (YY)YXXXX raid 6
================================
This is from experience at looking through various setups like this
I will verify if im correct or wrong with L3 tommorow
I would like to have X-RAID2 dual redundancy and have a mix of 3TB and 2TB disks available for use. My desire at first was to first use my 2TB disks since I've had those the longest but after reading through the responses, it sounds like I should be using at least 4x3TB and only then use the 2TB disks. With the recent sales on 3TB disks, I could load up all 6 slots with 3TB disks and then save the 2TB disks for an offline backup.
I recently expanded my Ultra 6 volume. I had 6x1.5TB disks installed and I'm using X-RAID2 dual-redundancy. I had to install 4x3TB drives before expansion took place.
Thats an initial setup where you need the 4 disks to start RAID 6 with mdadm software. However this doesnt cover the expansion topic where you only need 3.
????? I last did a factory default back on 4.2.12 (yes, that's right 4.2.12) in July 2010 with 6x1.5TB disks installed and configured the NAS to use X-RAID2 dual-redundancy. I added the 3TB disks late last year to expand my volume.
I would like to have X-RAID2 dual redundancy and have a mix of 3TB and 2TB disks available for use. My desire at first was to first use my 2TB disks since I've had those the longest but after reading through the responses, it sounds like I should be using at least 4x3TB and only then use the 2TB disks. With the recent sales on 3TB disks, I could load up all 6 slots with 3TB disks and then save the 2TB disks for an offline backup.
4x3TB+2x2TB or 6x3TB are best. I guess 5x3TB is also reasonable, leaving 1 slot open for future expansion.
