Hi kobiro & welcome to the forums.
I am looking for some assistance in backing up a set of drives that I can’t take down.
[…]
it is giving me a bunch of what I think are raid partitions instead of a drive name
three different issues here:
a - do you really want to backup the individual drives? Or rather the content of the RAID, which would be more usual?
By the names of the block devices, it looks like you’re running this on a hardware RAID controller, which likely won’t let you access the individual drives of that RAID set. And except for some data recovery situations, there should be no need for that, anyhow.
b - looking at your /proc/partitions, I see both, the “whole device” and the individual partitions. “c0d0” is “controller 0, raid drive 0”, with “c0d0p1”, “c0d0p2” and so on being “partition 1”, “partition 2” of that drive.
c - when it comes to backing up that data, a very important thing to consider are “caches” (application level and file system level) and consistency: When you’re using “dd” on a live block device, you do get the latest “blocks” from your device, but a file system cache (or application) may already have new content, which is just not yet written to disk. And additionally, while you’re reading your block device sequentially, new content may be written to the device not only in areas yet to be read by dd, but those you have already backed up. IOW, you end up with an inconsistent backup. Like adding new files to a directory (for example’s sake: file content written at the end of the block device, while the directory information is written in the already backed up part)
Is it possible to copy an entire raid to another drive using the dd tool?
Yes, since “a RAID” is nothing more than an ordinary block device, from the operating system’s point of view. But it may not be the most useful approach, depending on the type of data on the disk.
is there another option?
Backup up the content of a file system using i.e. “tar” would give easier access to individual files and won’t depend on a properly sized target device (think of a 400 GB block device with only a single 100 kB file on it… backup up the whole “disk” would be pretty ineffective).
And in case of a live system, you really need to pay attention to consistency issues, as described above.
Regards,
J