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My linux root OS device is /dev/sda, and my external hard drive is /dev/sdb (empty drive)

I don't want to loss data on /dev/sda, and setup raid level 0.

Is this possible?

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    Possible, but not advisable... Commented Sep 26, 2018 at 11:53
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    Raid 0 on ordinary disks is only advisable when you either have good backups or don't care about losing all your data. (I've seen raid 0 on top of multiple small raid 5 arrays, and it was only done because the users couldn't afford a proper large array). It sounds like you care about losing data; do you have backups? Commented Sep 26, 2018 at 12:04
  • Even if we have single disk, data loss is there...so what is the difference having a single disk or having raid-0 with 2 disks...? Commented Sep 26, 2018 at 12:09
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    With 2 disks in raid 0, you get twice the chance of data loss! Commented Sep 26, 2018 at 12:16
  • I am using just for testing to increase performance...How much probability can i expect of data loss (ie: 50%)and i which cases it to happen.. Commented Sep 26, 2018 at 12:23

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With RAID 0, your data is split in half (evens and odds) between the drives. In other words, there are chunks 1, 3, 5, .... etc. on the first drive, and a second group of chunks 2, 4, 6, etc. are on the second drive. If one of the drives dies, you've instantly lost 50% of the chunks. Imagine opening up your program and deleting every other line out of it. That's what happens when you lose a striped disk. Depending on the stripe size, you may be able to recover some data or even whole files out of the remaining disk (it's very possible that a 10KB file would be completely intact on one disk since your blocks should be larger than that). However, a file that's ten times your block size would have 5 blocks on each disk, meaning you just lost 50% of your file.

Important to note that you can't set up RAID 0 without formatting (initializing) the drives as RAID 0. You would have to back-up your data before creating the raid.

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    The question, I believe, is regarding setting up a RAID-0 configuration of two disks, while not wiping the data on one of the disks. Commented Sep 26, 2018 at 12:32
  • So its just same as using single disk(about losing data)....because here raid-0 is just a utility for using them as one.....that's it...so it is not increasing probability of losing data...Its just our fear loss or some tech phobia...right? Commented Sep 26, 2018 at 12:49
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    Hi @Akhil J. When you create the raid array it will erase the data currently on the drives you are using to build the "odds and evens" so you need to backup the data Commented Sep 26, 2018 at 12:55
  • By the way. RAID 0 has zero redundancy, meaning if only one of the disks fail, and you have lost all your data. I encourage you to find alternative solution for backing up your data such as RAID 1.where you can just convert your disk to dynamic, add the new disk and mirror it within disk management. You don't lose any data that way, unless you do something wrong. Commented Sep 26, 2018 at 12:58
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Why people don't understand statistical mathematics?

Almost all HDDs fail slowly - one bad (recoverable) sector at a time - giving the user plenty of opportunity to replace a failing drive - true of all single drives, stripe sets, and concatenations.

The odds of a catastrophic failure given the average HDD is something like 0.1% in the most liberal terms - likely it's more like 0.01%. Over 80% of catastrophic failures happen within the first month of use. That puts my numbers here at 0.02 and 0.002 respectively if the user is dealing with drives they've been using for a month or so - and according to the OP, at least one of them qualifies. Multiplying the drives by two does NOT increase the odds 200% - that's not how statistical math works. But even if it did that's still only 0.04% chance to fail unrecoverably. This is literally zero and two times zero is still zero.

I know it's popular for people to repeat this falsehood regarding RAID0 but get ahold of yourselves. RAID0 is likely the best most fitting solution option for gamers and other home computerists who typically store only very replicable files on their systems.

The average HDD these days does about 200MB/s for the first 80% of the platter surface. A two-drive RAID0 stripe does 380 to 390MB/s which is quite near the typical SSD but typically less than half the price per gigabyte - and available in HUGE storage sizes.

A three drive RAID0 composed to 3TB drives offers a NINE TERABYTE storage device capable of about 550MB/s costing less than $200. The same thing in SSD form start at $1,500 and are not noticeably faster! Nor all that much safer for that matter.

Unfortunately for the OP I do not know of a utility or application off hand which would allow you to create a RAID0 stripe without first formatting both drives. It absolutely is possible, I just do not know where to direct you.

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