RAID with different sized drives?

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LegoMyGeggo

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Dec 15, 2013
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Hi Guys,

I just bought a synology 4 bay NAS and have 4 drives (2 3TB drives and 2 4 TB drives). My question is would it be possible to combine 1 3TB and 1 4TB drive as 7 TB and then using RAID 1 to mirror that to the other two drives? Or would I be stuck at 6 TB since it would only conform to the smallest sized drive?

Thanks in advance!

G
 
Solution
laviniuc
for any basic raid you need 2 hdd (identical)

-raid 0 is meant for speed, each data block is spread between the 2 hdd-s. you get the sum of the space available on the 2 and about 50-75% speed increase since it's concomitant writes. if one fails the data on both is lost (each hdd has just half of the pieces of the puzzle which is your data)
-raid 1 is meant for reliability. each data block is written to both at the same time. you lose half of the capacity and the speed is the same as the slowest of them. if one drive fails you replace it and nothing happens.

combine the 2 raid solutions above and you get raid 01 (or 10) as in, data is written on both like on raid0 but also backed up on the second set of hdd's. if 1 drive fails it can...
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Benevolence

Benevolence

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Dec 2, 2013
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It can be done, however the raid size is restricted to the smallest drive in the array. It's generally frowned upon to use different drive types, let alone sizes for RAID, but it can be done if you don't mind sacrificing the extra space on your larger drive to do it. Your 3+4TB RAID would only be 6TB, and might suffer performance issues. If you have 2 3TB, and 2 4TB just combine the like sizes into two different RAID1 (or 0) arrays.
 
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LegoMyGeggo

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Thanks for all the responses guys :). One last dumb question. Since I received the drives as gifts, would it be easier to just return the 2 3TB drives and buy 2 more 4 TB drives to do one large 8 TB Raid 1? These are WD Red NAS drives if that helps as well. Or if there is a better configuration you recommend I am all ears :).
 
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LegoMyGeggo

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What would be the best configuration? Sorry I've been trying to read up on RAID since I got these and just have been kind of lost. I just want to backup my family files/photos/movies etc and have some kind of redundancy in case of HDD fails. Thanks again.
 
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laviniuc

laviniuc

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Nov 29, 2013
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for any basic raid you need 2 hdd (identical)

-raid 0 is meant for speed, each data block is spread between the 2 hdd-s. you get the sum of the space available on the 2 and about 50-75% speed increase since it's concomitant writes. if one fails the data on both is lost (each hdd has just half of the pieces of the puzzle which is your data)
-raid 1 is meant for reliability. each data block is written to both at the same time. you lose half of the capacity and the speed is the same as the slowest of them. if one drive fails you replace it and nothing happens.

combine the 2 raid solutions above and you get raid 01 (or 10) as in, data is written on both like on raid0 but also backed up on the second set of hdd's. if 1 drive fails it can always be replaced. if a second one fails before you replace the bad one it's a 33% chance to break the raid (if the fail is on the second pair of the raid1 keeping the other set of puzzle pieces data it's ok)

the problem in your case is that the second set is not the same size. so you can either raid1 each 2 identical drives and you get a 3tb and a 4td array or raid 01 and the 4tb ones would be used as 3tb drives and you get a 6tb raid 01. or get 2 new 4tb drives and you get a 8tb raid 01.
 
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LegoMyGeggo

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Haha I appreciate your patience with me. I never really understood how this RAID stuff works. But from your description, I guess to maximize my space I would b better off doing a RAID 01/10 with 4 4TB drives to achieve what I wanted. And since we're dealing with 4 drives, I don't think there would be much of a difference in terms of fault tolerance?

Regardless, I really appreciate all the help you guys gave me and your patience :).
 
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laviniuc

laviniuc

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yes. raid01(10) has the same fault tolerance (as in, you can lose 1 drive and 1 more from the 3 left at a 66% chance) regardless of capacity. if possible try to find the same hdd models as the 4 tb's that you intend to keep.

the other 3 tb hdd's you can always keep for critical stuff or backup onto them from the raid from time to time the really important stuff (plug them in another pc and copy to them manually the really important stuff). or raid 1 them in another pc for normal storage
 
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LegoMyGeggo

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Btw, one more question. If I set up my current 2 4TBs as RAID 1 and then buy the remaining two later down the line, can I expand it out later to do RAID 10 or do I have to set it like that initially (as in should I get the two drives this instant)?
 
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laviniuc

laviniuc

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it's possible to "grow" the raid, it's a bit complicated but possible. ofcourse you can always drop the raid completely and recreate since you can backup all the data to one of the 3 tb drives. i guess it depends on how much data you manage to fill up until you get the other new disks

http://www.burgundywall.com/tech/convert-raid1-to-raid10-with-lvm/
 
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