Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

http://forum.synology.com/wiki/index.php/What_is_Synology_Hybrid_RAID%3F

Synology is just Linux and uses LVM.

How do their tools automate LVM to achieve what they call their Hybrid Raid?

share|improve this question
    
You can try using BTRFS, it supports dynamic subvolumes... –  user173139 May 9 '13 at 18:07

2 Answers 2

It looks like the system splits up each drive into as many partitions as needed to create a series of RAID5 and/or RAID1 arrays that minimize the amount of unused space on the drives. Those RAID arrays then become physical volumes under LVM, which, in turn, presents all that storage as a single logical volume.

Current versions of mdadm do allow you to add devices to RAID5 arrays and to reshape RAID1's into RAID5's, so it is possible to add disks to this thing to grow the available storage "on the fly". Adding a new disk would be a matter of creating the appropriate partitions on the disk, and then adding its partitions to existing RAID5's and/or RAID1's, or creating new RAID1's with unused space from other disks. You can also increase your storage space by replacing a smaller disk with a larger one. I haven't thought too deeply about all the possible corner cases, but I imagine there will be a number of them.

Presumably, Synology has automated all this with their own custom programming, but I don't see why it couldn't be set up manually. Perhaps someone out there has already come up with the equivalent scripts? (I don't know.)

Keep in mind that this thing's failure mode is going to be just like RAID5: If a single drive fails, and then another one fails during the resync, bye-bye data. So I wouldn't use this configuration with more than, say, 5 or 6 drives, at the very most.

share|improve this answer

True in the past. However, as of Synology DSM 3.1, Synology Hybrid RAID will now have the ability for two redundant drives. This makes the Synology solution much more appealing to me, since I prefer to reuse older, excellent drives over buying four to six new drives every few years. This also allows for expansion by removing the smaller drives and replacing them with larger drives in the future. I find the technology highly compelling.

share|improve this answer
    
I think for SHR-2 they only use raid 6's though I do believe mdadm lets you also make a raid 1 with 3 disks to maintain 2 disk redundancy. Some insights can be garnered from using their raid calculator tool and putting in mixed sized disks. eg. put in 3x or 4x 2TB drives with 3x 3TB drives with SHR-2 and watch the unused space –  BeowulfNode42 Nov 7 '13 at 9:47
    
there are lots of comments around the net saying "raid 1 is only for 2 disks" this is not true with mdadm so a 5 disk system made from 2x 2TB and 3x 3TB could be made with a RAID 6 taking 2TB from each disk and a RAID 1 with the last TB on each of the 3TB disks to give a total of 7TB of usable storage with 2 disk redundacy. Though that extra 1TB on each of the 3TB drives may be required for expanding the drives later with some combo I haven't thought of. –  BeowulfNode42 Nov 7 '13 at 10:02

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.