sonofdbn Posted August 22, 2007 Share Posted August 22, 2007 Is there any place where we can find the actual disk size (as unRaid sees it) of hard disks? For example, if I buy two 500GB hard disks, one Seagate and one Hitachi, I'm almost certain they're not the same size when measured in bytes, and I also don't know which one is larger. The issue would be if, say, I have a Seagate 500GB as the parity drive and then buy a couple 500GB Hitachis, I might find that the Hitachis are "too big". Will unRaid totally not work with the Hitachis (assuming I keep the parity drive as it is), or will it just limit the storage capacity of the Hitachis? Quote Link to comment
Joe L. Posted August 23, 2007 Share Posted August 23, 2007 Log in via telnet and then type: df It will show you the sizes of all your mounted file systems. Quote Link to comment
sonofdbn Posted August 23, 2007 Author Share Posted August 23, 2007 I was thinking more of the problem of finding out the size before I buy the drives. Quote Link to comment
Joe L. Posted August 23, 2007 Share Posted August 23, 2007 I was thinking more of the problem of finding out the size before I buy the drives. It really does not matter. Let me explain. If a replacement or new drive is any bigger than your existing parity drive, the unRaid server will not start until you make the bigger drive the parity drive. If you are adding a new and bigger drive, to an existing array, even if only bigger by one byte, you can simply assign the new bigger drive as your parity drive and then restart the array. Parity will be calculated and written to it. Then, stop the array once more and assign the old parity drive as a data drive and re-start. It will be cleared, formatted, and added to the array. (I've not done this, but you might be able to do both steps at the same time. Your old parity drive would show up as unformatted, and it would be cleared first, a file-system built on it, and then parity calculated on the entire array.) If you are replacing a failed drive, and the new replacement drive happens to be slightly bigger than your existing parity drive, then... from what I've read, you can assign the new replacement drive as parity, and the old parity drive as your data drive. Tom referrers to this as a parity-swap operation. He describes how parity will first be copied from the old parity drive to the new, and then the failed disk's contents re-constructed on the old parity drive, now re-allocated for use as a data drive. In both cases, adding a new drive, and replacing a failed drive, the parity drive will end up being bigger or equal in size to your biggest data drive and it did not matter if the new/replacement drive was bigger than any in your existing array. Hope this helps... Joe L. Quote Link to comment
Billped Posted August 23, 2007 Share Posted August 23, 2007 Jane, you ign.... I think it does matter. For one, the additional time it takes to recalc (or copy) parity and rebuild the array means your system is unprotected for longer than it should be. Secondly, it means more personal interaction with the system which many of us are attempting to minimize ("set it and forget it"). To what extent this is important is something for each of us to figure out for ourselves. In the world of hardware raid, there are typically ways of playing with the size of drives to make this a non-issue, so if your new data drive is 1B bigger than your parity drive, you would just reduce the size of the data drive by 1B. I don't know if this is possible in SW implementations or not (perhaps during the formatting process it could create a small partition to keep the rest of the drive within the bounds set by the parity drive?) Bill Quote Link to comment
industrialarts Posted August 25, 2007 Share Posted August 25, 2007 I was thinking about this from a different perspective today. As appealing as it is to add the largest drives possible, you also stand to loose the biggest amount of data (in the event that the parity drive fails when a data drive fails, like from system failure or even a power drop out). So might it be better to add something smaller as you add drives? I realize there are several factors involved with adding drives, but when I upgrade my system, I might not purchase anything larger than 400G (my parity drive is 500G). And then I would never have to think about the parity drive. Just a thought industrialarts Quote Link to comment
parsec Posted August 25, 2007 Share Posted August 25, 2007 Paritydrive failure in itself do not give dataloss, just loss of protection. 400gig drives will "soon" seem way too small, and unraid gives you the opportunity to dynamically expand your datacapasity. The best cost/mb strategy is to buy the best HD deal along the way, depending on your needs. When you eventually run out of space in your cabinet or reach the 16 drives limit, you replace your 320 gig drive with the current discounted 4TB drives. /Rene Quote Link to comment
limetech Posted August 26, 2007 Share Posted August 26, 2007 Is there any place where we can find the actual disk size (as unRaid sees it) of hard disks? For example, if I buy two 500GB hard disks, one Seagate and one Hitachi, I'm almost certain they're not the same size when measured in bytes, and I also don't know which one is larger. The issue would be if, say, I have a Seagate 500GB as the parity drive and then buy a couple 500GB Hitachis, I might find that the Hitachis are "too big". Will unRaid totally not work with the Hitachis (assuming I keep the parity drive as it is), or will it just limit the storage capacity of the Hitachis? If you can find data sheets for the drives on the manufactures website they often will tell you precisely how many sectors there are. If you already bought them, just plug into your server and assign them as disk1, disk2, disk3 (ie, no parity). Then their exact size will be displayed on the Main page where you can decide which to use for parity. In any case, parity drive must be larger, or same size as all other drives. Quote Link to comment
industrialarts Posted August 28, 2007 Share Posted August 28, 2007 Paritydrive failure in itself do not give dataloss, just loss of protection. /Rene I understand your point, but what my concern is - in the event that both a data drive AND the parity drive were damaged, you would stand to lose more data with larger drives. If a power supply were to fail or just have a long enough period of bad line voltage, then this could be more than just a theoretical concern. And I get the feeling that a lot of the UNRAID users out there are not conditioning the AC line voltage for their server, once again opening up the possibility of multiple drive errors. It would be great if there were a way to back up the parity drive (this from the Department of Redundancy Department) industrialarts Quote Link to comment
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