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XRAID turned RAID5 into RAID6 when adding a drive
When I added a drive, my RAID5 config changed to RAID6. Is it supposed to do that?
36 Replies
When you go past 6 disks xraid will turn your RAID5 to a RAID6
"X-RAID® dynamically changes raid RAID1 for 1 - 2 drives. RAID5 for 3 - 6 drives. RAID6 for 7+ drives"
You can try out different setups here:
Danthem wrote:
"X-RAID® dynamically changes raid RAID1 for 1 - 2 drives. RAID5 for 3 - 6 drives. RAID6 for 7+ drives"
I agree with the logic (though I wonder what would happen if that conversion required shrinking the volume size - which could be required if the drives aren't the same size).
But I think there should be a confirmation on the UI before the conversion happens.
It's not sensible to use RAID-5 with that many disks.
The volume wouldn't be shrunk. Attempting to shrink a volume is dangerous.
So, after some research, I confirm that X-RAID doesn't treat 6 HDDs the same way depending on the number of bays. So it changes a little bit the scenarios.
If the chassis has 6 bays or less, it won't go to RAID6. If the chassis has more than 6 bays, it goes to RAID6 starting at the sixth disk.
X-RAID doesn't create volumes accross chassis and expansion chassis, to there is no situation where you can start with six HDDs RAID5 and add a HDD to the volume.
3) If you Factory Default with four or five HDDs, the same thing will happen. Main RAID is RAID5. X-RAID will create secondary RAIDs where there is a possibility with at least one device redundancy. The BTRFS volume capacity is the aggregated capacity of all the RAIDs.
Example:
2x1TB + 2x2TB + 1x4TB -> md127 is a RAID5 of 5 partitions of 1TB (4TB capacity, 1TB parity). md126 is a RAID5 of 3 partitions of 1TB (2TB capacity, 1TB parity), the top 2TB on the 4TB HDD will remain unused. BTRFS volume capacity is 6TB.
3bis) If the unit has 6 bays or less and you Factory Default with six HDDs, it does the same as 3, so based on RAID5.
Example:
2x1TB + 3x2TB -> md127 is a RAID5 of 6 partitions of 1TB (5TB capacity, 1TB parity). md126 is a RAID5 of 3 partitions of 1TB (2TB capacity, 1TB parity). BTRFS volume capacity is 7TB.
3ter) If the unit has more than 6 bays and you Factory Default with six HDDs, X-RAID will base the RAIDs onto dual redundancy, so RAID6.
Example:
2x1TB + 4x2TB -> md127 is a RAID6 of 6 partitions of 1TB (4TB capacity, 2TB parity). md126 is a RAID5 of 4 partitions of 1TB (2TB capacity, 2TB parity). BTRFS volume capacity is 7TB.
3x1TB + 3x2TB -> I need to confirm that.
4) If you Factory Default with seven HDDs or more, the same thing will happen but with RAID6 and two devices redundancy.
Example:
12x1TB -> md127 is a RAID6 of 12 partitions of 1TB (10TB capacity, 2TB parity), BTRFS volume capacity is 10TB.
10x1TB + 2x2TB -> md127 is a RAID6 of 12 partitions of 1TB (10TB capacity, 2TB parity). X-RAID can't create a RAID with two devices redundancy on the unused 1TB of both 2TB HDDs. BTRFS volume capacity is 10TB.
9x1TB + 3x2TB -> I need to confirm that.
8x1TB + 4x2TB -> md127 is a RAID6 of 12 partitions of 1TB (10TB capacity, 2TB parity). md126 is a RAID6 of 4 partitions of 1TB (2TB capacity, 2TB parity). BTRFS volume capacity is 12TB.
8) There is no situation with X-RAID where you can have a six HDDs RAID5 and add a seventh HDDs. If you have more than six slots, your six HDDs are in RAID6. If you have six slots or less, you six HDDs are in RAID5 and you can't go to RAID6.
8a) If the unit has more than 6 bays, starting with 3x1TB + 2x2TB. md127 is a RAID5 of 5 partitions of 1TB (4TB capacity, 1TB parity). md126 is a RAID1 of 2 partitions of 1TB (1TB capacity, 1TB parity). BTRFS volume capacity is 5TB.
If you add a 1TB HDD, you have 4x1TB + 2x2TB. md127 should be reshaped to a RAID6 of 6 partitions of 1TB (4TB capacity, 1TB parity). But md126 can't be reshaped to a RAID6 as there are only two partitions for it and no unused capacity on the new HDD. I need to confirm what happens in this case.
If reshape to RAID6 does occur on md127, you end up with a two devices redundancy on primary raid, but remain with a one device redundancy on secondary raid. Which is not good in my opinion.
If reshape to RAID6 doesn't occur on md127, then what happens? Expansion in a RAID5?
-> I need to confirm that.
8b) If the unit has more than 6 bays, starting with 4x1TB + 2x2TB. md127 is a RAID6 of 6 partitions of 1TB (4TB capacity, 2TB parity). BTRFS volume capacity is 4TB.
If you add a 2TB HDD, you have 4x1TB + 3x2TB. md127 should expand to a RAID6 of 7 partitions of 1TB (5TB capacity, 2TB parity). I believe X-RAID can't create a RAID6 on the three last HDDs unused capacity. BTRFS volume capacity is 5TB.
-> I need to confirm that, but vertical expansion rules give a minimum of 4 HDDs in RAID6).
8c) (following 8b) If the unit has more than 6 bays, starting with 4x1TB + 2x2TB. md127 is a RAID6 of 6 partitions of 1TB (4TB capacity, 2TB parity). BTRFS volume capacity is 4TB.
If you add a 2TB HDD, you have 4x1TB + 4x2TB. md127 should expand to a RAID6 of 8 partitions of 1TB (6TB capacity, 2TB parity). X-RAID creates md126 as a RAID6 of 4 partitions of 1TB (capacity 2TB, parity 2TB). BTRFS volume capacity is 8TB.
---
Irrelevant now, but it seems that X-RAID behaves differently on RAIDiator 4.2 and OS6. On RAIDiator 4.2, there were situations where you could have RAID5 on two devices. But on OS6, secondary raid on two devices in RAID1.
Example:
md2 : active raid5 sda3[0] sdb3[1] 1948792704 blocks super 1.2 level 5, 64k chunk, algorithm 2 [2/2] [UU]---
Also, X-RAID was called X-RAID on RAIDiator 4.1, X-RAID2 on RAIDiator 4.2, and X-RAID again on OS6.
First of all, thx for the detailed reply and research. Much appreciated.
jak0lantash wrote:
8a) If the unit has more than 6 bays, starting with 3x1TB + 2x2TB. md127 is a RAID5 of 5 partitions of 1TB (4TB capacity, 1TB parity). md126 is a RAID1 of 2 partitions of 1TB (1TB capacity, 1TB parity). BTRFS volume capacity is 5TB.
If you add a 1TB HDD, you have 4x1TB + 2x2TB. md127 should be reshaped to a RAID6 of 6 partitions of 1TB (4TB capacity, 1TB parity). But md126 can't be reshaped to a RAID6 as there are only two partitions for it and no unused capacity on the new HDD. I need to confirm what happens in this case.
If reshape to RAID6 does occur on md127, you end up with a two devices redundancy on primary raid, but remain with a one device redundancy on secondary raid. Which is not good in my opinion.
It's not good in my opinion either, which loops back to the original question. It isn't dual redundancy unless both md126 and md127 are both dual redundancy. If md126 is RAID-5, the array can recover from some combinations of 2-drive failures, it can't recover from them all.
Also,I'd expect a factory reset with 7 drives still in place should always give me the same volume size I had before (although the details of the underlying RAID layers can be different, depending on the history). At this point its hard to know if that will happen or not (its still on your confirm list for the factory reset cases).
However, there is a problem with 8a. The 6th drive would need to be 2 TB in order to be added to the array. XRAID always limits new disks to be >= the largest disk in the array. Disk replacements can match the size they are replacing.
There is problem with 8c also - as written it goes from 6 drives to 8 (though only a single 2 TB drive was added).
Sorry, bad copy/paste
(corrected) 8c) (following 8b) If the unit has more than 6 bays, starting with 4x1TB + 3x2TB. md127 is a RAID6 of 6 partitions of 1TB (4TB capacity, 2TB parity). There is unused capacity on both 2TB HDDs. BTRFS volume capacity is 4TB.
If you add a 2TB HDD, you have 4x1TB + 4x2TB. md127 should expand to a RAID6 of 8 partitions of 1TB (6TB capacity, 2TB parity). X-RAID creates md126 as a RAID6 of 4 partitions of 1TB (capacity 2TB, parity 2TB). BTRFS volume capacity is 8TB.
StephenB wrote:However, there is a problem with 8a. The 6th drive would need to be 2 TB in order to be added to the array. XRAID always limits new disks to be >= the largest disk in the array. Disk replacements can match the size they are replacing.
For HDD swap, I agree. For horizontal expansion, I don't thing this is actually true.
8d) Factory Default with 1x1TB + 1x2TB HDDs. md127 is a RAID1 of 2 partitions of 1TB (1TB capacity, 1TB mirror). The 2TB HDD has unused capacity. BTRFS volume capacity is 1TB.
If you add a 1TB HDD, you have 2x1TB + 1x2TB. I believe md127 should reshape to a RAID5 of 3 partitions of 1TB (2TB capacity, 1TB parity). The 2TB HDD has unused capacity. BTRFS volume capacity is 2TB.
This is what you would get if you Factory Default in that HDD configuration.
--> I'll confirm that.
8e) Factory Default with 1x1TB + 2x2TB HDDs. md127 is a RAID5 of 3 partitions of 1TB (2TB capacity, 1TB parity). md126 is a RAID1 of 2 partitions of 1TB (1TB capacity, 1TB mirror). BTRFS volume capacity is 3TB.
If you add a 1TB HDD, you have 2x1TB + 2x2TB. I believe md127 should expand to RAID5 of 4 partitions of 1TB (3TB capacity, 1TB parity). md126 remains a RAID1 of 2 partitions of 1TB (1TB capacity, 1TB mirror). BTRFS volume capacity is 4TB.
This is what you would get if you Factory Default in that HDD configuration.
--> I'll confirm that.
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