Two newbie RAID 1 questions

[Trizik]

1) Does RAID 1 copy data on-the-fly? Meaning if I copy new data to a RAID 1 setup, do both drives write the data instantaneously?

2) How does RAID 1 decide which drive has desirable data? If I were to RAID 1 two drives, remove them from the RAID, copy a few different files to each drive, then put them back into the RAID 1 setup, which drive keeps its data?

 

[bunker]

1) yes, the writes are essentially simultaneous.

2) IIRC, the first drive you put into the raid will be the "master" (for lack of a better term), the second drive will be overwritten with whatever is on the first.

 

[shoRunner]

1) yes it is instant and seemlessly handled by the raid controller

2) it'd probably f* up your raid array

 

[Matthias99]

Originally posted by: Trizik
1) Does RAID 1 copy data on-the-fly? Meaning if I copy new data to a RAID 1 setup, do both drives write the data instantaneously?

Yes... that would be the entire point of RAID1.

Your computer sees an N-drive RAID1 array as a single virtual disk with 1/N times the capacity of each drive in the array. Any data you write to the virtual disk is written to all N mirrors.

2) How does RAID 1 decide which drive has desirable data? If I were to RAID 1 two drives, remove them from the RAID, copy a few different files to each drive, then put them back into the RAID 1 setup, which drive keeps its data?

You can't do that. If you remove a drive from the array, all the data on that drive is no longer valid -- and when you put it back in, the contents of the remaining drive/drives will be used to repopulate the data on the drive that was just added. If you break the array, modify both drives, and put it back together -- the controller would have no idea what to do. Plus, you usually can't just pull a drive out of a RAID1 and access it like a normal hard drive.

 

[Trizik]

thanks for the replies. so if one drive crashed in a RAID 1 setup, it wouldn't be possible to access the working drive? (even if i were to remove it from the RAID 1 setup?)

 

[Matthias99]

Originally posted by: Trizik
so if one drive crashed in a RAID 1 setup, it wouldn't be possible to access the working drive? (even if i were to remove it from the RAID 1 setup?)

No... the array would keep working like nothing happened, and then you could swap out the broken drive and sync them back up. That is the entire point of having RAID1.

 

[bunker]

Originally posted by: Trizik
thanks for the replies. so if one drive crashed in a RAID 1 setup, it wouldn't be possible to access the working drive? (even if i were to remove it from the RAID 1 setup?)

In order to access the working drive you need to leave it in raid. You can leave it in raid 1 with just the one drive until you're able to replace the dead one.