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Originally Posted by
c.wakeman
How long are we talking? For ~200+ GBs, hours, days? My window machine is a core2 duo e8600 running at 3.33 GHz with 3.25 GB RAM.
The limit is mostly disk speed. Since you're reading and writing to the same disk, the speed is reduced. The time might approach double-digit hours.
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I think the drive comes XFS base, reformatting to another format shouldn't be too difficult. What would you suggest, NTFS?
Definitely not NTFS. I already noted that the "easy" ntfs driver is read-only. There's a better one available, but even the "good" one is still incomplete -- and intentionally difficult to get. They had to do that for their own sanity. People were ignoring an amazing quantity of red flashing "USE AT YOUR OWN RISK" warnings and getting all mad when important data was lost.
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Does this command just see if they are there or load them if they are? Is this safe, stability wise? I don't want to make changes that jeopardize the safety of the data prior to having it backed up...
All it does is load the ability to understand XFS filesystems, if available. It's safe.
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By that do you mean it doesn't care what files are on the drive or what format it is, or both?
All dd does is this:
- Read sector 0 from /dev/sda
- Write sector 0 to /dev/sdb
- Read sector 1 from /dev/sda
- Write sector 1 to /dev/sdb
- ...
- Read sector N from /dev/sda
- Write sector N to /dev/sdb
- End of file. Quit.
It dumps the contents of sda into sdb with complete ignorance of the meaning of data in sda and complete disregard for any current contents of sdb. (getting them backwards would be very bad. Hence the chmod step to prevent disaster.)
The way disks and partitions work means it doesn't have to understand what's in sda is to make a perfect copy. Dumping it raw replicates everything with perfection, including boot sectors, boot loaders, partition layouts, partition types, hidden recovery partitions, empty space, remnants of deleted files sitting in empty space, etc, including any things you didn't know about or didn't care about. The only caveat is the destination disk must be of equal or larger size than the source.
This single-minded blindness means it can even clone a system alien to it. Contents that seem like nothing but garbage will be replicated faithfully. I regularly do replications of Windows machines from Linux disks when installing a larger hard drive -- clone the old disk onto the new one and enlarge the partition later. I've done replications with macs once or twice.
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So what you're saying is, I would make a mirror of the entire system hard drive, and then weekly, could do backups, more similar to the online style, where I just upload file changes?
Yeah.
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Choosing between these options should all be kept in the context that, at some point, I am going to ideally be installing the RAID 1 backup to do nightly backups. At that point, the external drive will be either kept in a separate location in the office or as you have suggested kept off-site (if possible) and brought in to do weekly backups.
An up-to-date clone of the server would be a nice thing to have handy if you're trying to set up a RAID. If the RAID controller does anything unexpected like blank your drives when you configure an array, you can dub your backup back onto it to get everything back.
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When I do install the RAID system, is it better to have them simply backup data files or for them to act as a mirrored system? Planning ahead could help determine what should be done now.
It'd hardly be a RAID if you didn't mirror or strip or extend the disks in some way. It'd just be an extra hard drive.
If you want to keep it simple, a hardware RAID mirror would be simple. It'd act like the system you already have, a one-disk system, and all the advice I've given you so far would still apply to it. There's more complicated, fault-tolerant setups like raid5, but this takes a lot more disks and hardware, money that's probably better spent on things like a good uninterruptible power supply and a fire safe for your backups.
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Finally, if I really wanted to, could I do both?
Absolutely. A hardware mirror can swallow a single-disk failure and keep going, plus weekly backups to your external drive can save you from more drastic things.