February 14, 201412 yr Noob question Short and sweet, my google-fu failed me this once. Is there a relationship to the capacity of my parity drive to my data array? I have 3 500 gb hdd's. I would like to know the relationship to the capacity of the parity drive to the storage array. this is what i have to work with right now. used parts, old puters etc. free stuff... mid tower case with 6 hdd slots 939 processor 64 bit 500 watt ps with 18 amps on the 12 volt rail out of an old dell duo core workstation. 120 mm fan for cooling. 4 slots for ram, currently filled with 512 mb sticks, total 2 gig Hate to ask people, an answer would be nice, better a point to the right manual ty in advance
February 14, 201412 yr If I understand you correctly, the parity drive has to be bigger or at least equally sized as to biggest data drive in your array. In your case bigger or equal to 500gb. Want to put in bigger data drives, need to put in a bigger parity drive first :-) And welcome to unRAID :-)
February 14, 201412 yr The parity drive is ignored when calculating space on the array - simply add together the sizes of all the data drives. The only rule on the parity drive is that it must be the same size (or larger) as the largest data drive.
February 14, 201412 yr Right. one 500 Meg parity drive can support many 500 Meg data drives. If you're planning to buy larger drives in the future (current prices are way down...multi Terabyte drives are most cost effective these days), then plan ahead...your first large drive would have to be the parity drive, to support future larger data drives. You can mix and match sizes of data drives, but the parity drive must be as large as the largest single data drive.
March 20, 201412 yr Say i have 4 x 2tb drive + 1 x 2tb drive. approximately i have 8tb of usable space and i filled it up with say 7tb of data. It amazes me how 1 single drive able to hold information of 7tb of data?
March 20, 201412 yr Say i have 4 x 2tb drive + 1 x 2tb drive. approximately i have 8tb of usable space and i filled it up with say 7tb of data. It amazes me how 1 single drive able to hold information of 7tb of data? No, you have 7TB of usable space. The parity drive must be >= the largest data drive; so one of the 2TB drives has to be the parity drive. This leaves 3 2TB drives plus a 1TB drive for data -- a total of 7TB. As noted earlier, the requirement that parity is >= the largest data drive is the only constraint. For all the other drives, you just add up the space to get the total amount of available storage space.
March 20, 201412 yr Say i have 4 x 2tb drive + 1 x 2tb drive. approximately i have 8tb of usable space and i filled it up with say 7tb of data. It amazes me how 1 single drive able to hold information of 7tb of data? I know it seems a little like magic for one parity disk to be able to protect 7 data disks. To understand you need to better understand how parity works. Check out this post that I wrote a while back that tries to explain. It was written when unRaid supported fewer drives than today, but parity works the exact same way. Explanation of unRaid parity If you buy a new drive larger than your parity, you can make the new drive your parity drive, and convert your parity drive into a data drive. This is something most every unRAID user has done at least once. I started with 500G drives and updated parity for 750G, 1T drives, 1.5T drives, 2T drives, 3T drives and most recently 4T drives. If you think about it for a minute, you realize that buying a single, let's say, 2T drive is no better than a 500G if all of your other drives are 500G, but if you bought 2, 2T drives, then you'd see the benefit. If you look in my signature you'll find a section called Best of the Forums. Although a little dated (sorry about that, I have not maintained it in a while but hope to soon), it is a collection of posts by me and others that answer lots of questions about how unRaid works, how to maintain your array, perform advanced functions (like loading a Windows disk onto your unRAID server to more quickly copy data to your array), and lots of others. I quickly found the link on parity above by going there. Happy reading.
March 20, 201412 yr Say i have 4 x 2tb drive + 1 x 2tb drive. approximately i have 8tb of usable space and i filled it up with say 7tb of data. It amazes me how 1 single drive able to hold information of 7tb of data? It is not the single parity drive, it is the parity drive plus the data on all of the other drives that allows a single drive to be rebuilt. I think understanding this is critical because it helps everything make more sense. If you understand this you are less likely to make a mistake when it comes time to change anything about your array, whether adding a disk, upgrading a disk, or rebuilding a disk.
March 20, 201412 yr Say i have 4 x 2tb drive + 1 x 2tb drive. approximately i have 8tb of usable space and i filled it up with say 7tb of data. It amazes me how 1 single drive able to hold information of 7tb of data? No, you have 7TB of usable space. The parity drive must be >= the largest data drive; so one of the 2TB drives has to be the parity drive. This leaves 3 2TB drives plus a 1TB drive for data -- a total of 7TB. As noted earlier, the requirement that parity is >= the largest data drive is the only constraint. For all the other drives, you just add up the space to get the total amount of available storage space. Surely 4x2TB + 1x2TB = 5x2TB = 10TB of which one 2TB drive is parity. Remainder is therefore 4x2TB = 8TB, 7TB if which is utilised as the OP said. Just playing the 'pedant' card ...
March 20, 201412 yr Say i have 4 x 2tb drive + 1 x 2tb drive. approximately i have 8tb of usable space and i filled it up with say 7tb of data. It amazes me how 1 single drive able to hold information of 7tb of data? No, you have 7TB of usable space. The parity drive must be >= the largest data drive; so one of the 2TB drives has to be the parity drive. This leaves 3 2TB drives plus a 1TB drive for data -- a total of 7TB. As noted earlier, the requirement that parity is >= the largest data drive is the only constraint. For all the other drives, you just add up the space to get the total amount of available storage space. Surely 4x2TB + 1x2TB = 5x2TB = 10TB of which one 2TB drive is parity. Remainder is therefore 4x2TB = 8TB, 7TB if which is utilised as the OP said. Just playing the 'pedant' card ... Obviously that's right => My mind [in the wee hours ] somehow "thought" 4 x 2TB plus 1 x 1TB ... even though what I quoted was correct [My mistake is obvious if you read what I wrote -- I said "plus a 1TB drive" ]. Not sure why he listed them as 4 x 2TB + 1 x 2TB instead of 5 x 2TB
March 20, 201412 yr Just me being pedantic ... i apologise. Certainly nothing to apologize for -- you were right !!
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