All questions about RAID 1+0

@smayer97 

I am consolidating all your questions into one response. I want to check one thing before posting this. And I have made an FAQ, I am adding to our knowledge base online.

@smayer97 

Here is the FAQ we created in response to your queries.

https://software.owc.com/knowledge-base/softraid-raid-10-raid-10-faq /"> https://software.owc.com/knowledge-base/softraid-raid-10-raid-10-faq/

Posted by: @softraid-support

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@smayer97 

Here is the FAQ we created in response to your queries.

https://software.owc.com/knowledge-base/softraid-raid-10-raid-10-faq /"> https://software.owc.com/knowledge-base/softraid-raid-10-raid-10-faq/

That's great.

Posted by: @smayer97

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What are the ways to create a RAID 1+0 volume?

First, you need a minimum of 4 drives, and always in pairs, or increments of 2. 

There are 3 ways:

1. create the volume from scratch.

2. convert from a RAID 0 by connecting the extra drives and use the Convert function.

3. convert from an AppleRAID 1+0 using the Convert function.

Based on the FAQ created, and so someone reading this thread does not get the wrong information, SoftRAID STILL does not support converting AppleRAID 1+0.

Does this also mean that SoftRAID does not support converting from SoftRAID 1+0 to AppleRAID 1+0?

Posted by: @smayer97

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Can a RAID 1+0 be converted to to a RAID 1?

No. SoftRAID cannot do this. But you can do this in multiple steps:

1. remove the extra "mirrored" drives using the Remove function. This will leave you with a RAID 0 configuration. 

2. create a RAID 1 using the removed drives. Note the capacity may be different that the original volume, depending on how many drives you remove.

3. Copy the data from the from the RAID 0 to the RAID 1.

The FAQ says "Can a RAID 1+0 be converted to a RAID 1?

No. SoftRAID does not support converting a RAID 1+0 to a RAID 1.

Workaround:

• Convert the RAID 1+0 volume to RAID 0
• Create a RAID 1 using the two drives removed during conversion
• Copy data from the RAID 0 to the RAID 1
• Repurpose the remaining drives"

Does this mean that the Remove function cannot be used for this purpose?

The above assumes there are only 4 drives to start. Should there be mention that the R1 may be smaller, depending on the number of drives removed, even using the Convert function?

Re: "Can a RAID 1 be converted to a RAID 1+0?

No. SoftRAID does not support converting a RAID 1 directly to RAID 1+0.

Workaround:

• Create a RAID 0 using two additional initialized drives
• Copy data to the new RAID 0
• Delete the original RAID 1
• Use the Convert function to convert the RAID 0 to RAID 1+0
• The volume will automatically begin rebuilding"

Here too it is assumed that the R1 only has two drives. I suggest removing the reference to only two drives. 

"Can a RAID 5 be converted to RAID 0?

No. SoftRAID does not support this conversion."

Though SoftRAID cannot do this directly, it turns out this can be done IF one condition is met. I have created the math to figure this out. The net result is straightforward formula. See my post here https://forums.softraid.com/converting-volumes/convert-raid5-to-raid0-stripe/#post-24840

The net it is that if the RAID 5 data is ≤ X * n * (n-1) / (2*n -1), where X = the size of the drive, and n is the number of drives in the RAID 5, there is a work around. (As an example, if an R5 has n = 3 drives, and X = 6TB per drive (so the original R5 = 12 TB), then if the data in the R5 is ≤ 6 * 3 * ( 3 - 1) / ( 2 * 3 - 1) = 7.2TB, the work around I show in that thread can work. 

You may want to add this to your FAQ.

The above is also a solution to being able to remove one drive from a RAID 5 to convert it to a RAID 0. 

AND/OR, once converted to a RAID 0, the Convert function can be used to convert the RAID 0 to a RAID 1+0.

So you can go from a 3-drive R5 to a 4-drive or 6-drive R1+0

(sorry, actually you do not need this work around to convert to a 6-drive RAID 1+0 since you can use the 3 new drives to create a RAID 0, copy the RAID 5 to the RAID 0 then convert to a RAID 1+0).

BUT, the work around is useful to go from a 3-drive R5 to a 4-drive R1+0, a 4-drive R5 to a 6-drive R1+0, a 5-drive R5 to a 8-drive R1+0, 6 to 10, 7 to 12, 8 to 14, and 9 to 16 (SoftRAID's max). 

Posted by: @smayer97

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@softraid-support Is it possible to resize a RAID 1+0 to a larger volume, if there is room on the drives?

The FAQ says, "Can you increase the capacity of a RAID 1+0 by adding drives?

No. SoftRAID does not support expanding RAID 1+0 by adding drives.

To increase capacity:

• Create a new volume and migrate data"

The above would require unmounting the original RAID 1+0 while copying the data to the new RAID, so no data is changed during the operation.

If I understand the functionality of SoftRAID correctly, I believe there is a way to minimize downtime. If you swap out one drive at a time wit a large drive and allow each one to rebuild before swapping out the next one, at the end, you would only need to unmount the RAID just long enough to expand the RAID to fill the new drives.

You could even cut down the rebuild time by swapping out all of the mirrored drives, cutting the rebuild time almost in half.

Correct?

Posted by: @smayer97

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@softraid-support With 6 drives or more, there are two possible configurations for a RAID 1+0, either 2 stripes of 3 drives mirrored, or 3 stripes of 2 drives mirrored. Does SoftRAID support both configurations? 

The FAQ says, "Are different RAID 1+0 configurations supported with 6 or more drives?

SoftRAID uses a single RAID 1+0 layout.

• Any even number of drives (up to 16) can be used
• You can control mirror pair assignments by selecting which disks are paired together during creation
• This provides some flexibility, but alternate RAID layouts are not exposed as separate configuration options"

Can you elaborate on the 2nd and 3rd bullet, as I am unclear what the flexibility is, especially if the "layouts are not exposed as separate configuration options".

As an example, is it possible to have a RAID 1+0 with 2 stripes of 3 drives mirrored? If it does, this has the potential to behave like a multi-drive RAID 1 and theoretically allow the removal of at least one mirrored stripe set for offsite storage. Does SoftRAID allow any of this?

Once I better understand this, I may have a follow-on question about whether SoftRAID can handle adding drives to a RAID 1+0 and how it handles it (I read  the FAQ answer and get that you cannot add capacity to a RAID 1+0 by adding drives). 

re: the FAQ says, "What happens when a single drive fails in a RAID 1+0?

• The volume remains mounted in a degraded state
• All remaining drives continue to be used
• When the failed drive is replaced, only that mirror member is rebuilt, not the entire volume"

This seems clear but just to make sure I understand, when a drive fails, the remaining mirrored slices actually continue to be updated?

Does this also mean that the mirrored slices continue to be benefit from some speed benefit from reading from available mirrored slices, so a sort of 3-drive RAID 1+0 config?  

re: converting between AppleRAID 1+0 and SoftRAID 1+0, what is the limitation to implementing this?

@smayer97 
No, we do not currently support converting Apple RAID, and will not, as there is no consistent way to implement an Apple RAID 1+0. The Apple RAID 1+0 does not even work smoothly, its not possible for normal users to figure out, so we are not going to invest the resources into making sure it works. I will remove that from the FAQ. I think it was left over from your questions and missed that.

@smayer97 
"This seems clear but just to make sure I understand, when a drive fails, the remaining mirrored slices actually continue to be updated?

Does this also mean that the mirrored slices continue to be benefit from some speed benefit from reading from available mirrored slices, so a sort of 3-drive RAID 1+0 config? "

All disks that are still connected will be updated as new writes occur. When the volume rebuilds, all this is put together correctly.
Depending on the drives cache design, there may or may not be additional read benefits to a mirror. We once tweaked the driver for maximizing reads, but it only worked for the specific drives we optimized them for.  The "read ahead" cache's eliminate the benefit of "striped reads".