January 24, 201412 yr I've decided to try Unraid because of it's unique parity system. I like Raid5 but rebuilds can be scary. Unraid's softraid without stripes is awesome. I love the idea that the drives are readable individually. So I built a raid with 2 WD's and one Segate. The WD's are like 5 megabytes larger than the Seagate. So I'm using one of the WD's for parity and a very slightly smaller array. Recently I pulled an old WD and I want to replace the Seagate. Will the array readjust it's self? Disk1 Seagate 199GB Disk2 WD 200GB Parity WD 200GB Array 398GB Can I replace the Seagate with another 200GB WD and have a 400GB array?
January 24, 201412 yr You replace the drive and start the array and tell it to rebuild the replaced disk and the data is placed onto the new disk. Just don't use the new config or it will "forget" about the data on the Seagate disk.
January 24, 201412 yr Wouldn't I have to reconfigure the array and lose the data? No ... that's the whole idea of fault-tolerance !! You can simply replace the Seagate with a 200GB WD and it will rebuild the drive on the new larger drive. It hardly seems worth doing for 1GB, but if you're just "playing" for learning purposes, it would certainly give you the opportunity to see how the rebuild works.
January 24, 201412 yr Author I guess I wasn't clear. Parity 200GB WD Disk1 200GB WD Disk2 199GB Seagate Array 398. Which could mean that I'm only using 199GB on the two WD's. So putting a 200GB WD in with the other 2 would make it 199GB also correct? Unless I reconfigured the Array. Right?
January 24, 201412 yr I guess I wasn't clear. Parity 200GB WD Disk1 200GB WD Disk2 199GB Seagate Array 398. Which could mean that I'm only using 199GB on the two WD's. So putting a 200GB WD in with the other 2 would make it 199GB also correct? Unless I reconfigured the Array. Right? u sure about that... is should read 199... but its a small difference... nothing i would be concered about
January 24, 201412 yr I guess I wasn't clear. Parity 200GB WD Disk1 200GB WD Disk2 199GB Seagate Array 398. Which could mean that I'm only using 199GB on the two WD's. So putting a 200GB WD in with the other 2 would make it 199GB also correct? Unless I reconfigured the Array. Right? No, you're not understanding UnRAID. With that configuration you're using all of both Disk1 and Disk2 ... a total of 399GB. If you replace Disk2 with a 200GB drive, you don't have to change anything ... UnRAID will automatically rebuild Disk2 so you don't lose any data; and will expand it to the new size (200GB) ... so you'll then have a total of 400GB. i.e. a gain of 1GB. As I noted above, hardly seems worth the trouble
January 24, 201412 yr Author Got ya. It's not the room so much as the Segate runs really slow and hot and it is nice to have all the drives the same size.
January 24, 201412 yr unRAID allows any mix of drive sizes. So, for DATA you could have: Drive 1 = 200 Gig Drive 2 = 500 Gig Drive 3 = 120 Gig Total Data available = 820 Gig. Parity Drive = 1000 Gig The PARITY DRIVE must always be as LARGE as or LARGER than any single DATA drive. The PARITY drive has the error correction needed which spans across all the disks, regardless of their sizes. In the above setup, if you swap out the 120 Gig drive and insert a 250 Gig Drive, available DATA will become 950 Gigs. The Parity drive will see the new serial number for Drive 3...when you start the array, it will 'rebuild' Drive 3 from the error correction data. The original drive's 120 Gigs of data will be written to the new drive.
January 24, 201412 yr Thats pretty amazing. I have to get my head out of the idea of stripes. Yes. Its a very neat implementation. Its a JBOD with an added checksum disk (parity). That allows any disk to fail and be rebuilt should it be needed. If two disks fail simultaneously, there's no good recovery, but all data on the good disks survives intact.
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