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LarryM

Disks and raid

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Got notice that my Helios 4 is on it's way.  Yay!  But I have a question that I don't see here.  I followed the topic of creating, I believe it was a raid 10 with four disks, and I think that's where I want to end up, but I only have two drives right now.  Can I go ahead and start with just the two, and easily and the other two at a later date?  Or would I be better off waiting until I can get the other two drives?

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My recommendation would be to stay clear of raid configurations. With modern disk sizes the rebuild times are so long that the probability of a second disk failing during the rebuild becomes significant, and when that happens you're looking at a world of hurt.  Sure, use raid 0 if you need the performance and can tolerate the doubled failure rate, but I'd recommend using a straightforward rsync cron job to do backups to a completely different drive (as in different manufacturer/size or at the very least batch) rather than rely on any form of raid for reliability. Same applies to overly complicated LVM setups - in principle you can keep everything organized with LVM stripes and replicas, but in practice it's way too easy to loose track of things and have multiple dependencies that you weren't aware of. Having just suffered a 2 disk failure on a complex LVM setup, I don't intend to go there again. Label all your disks with their install date and replace them at intervals that match your risk tolerance.

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On January 30, 2018 at 6:22 PM, LarryM said:

Got notice that my Helios 4 is on it's way.  Yay!  But I have a question that I don't see here.  I followed the topic of creating, I believe it was a raid 10 with four disks, and I think that's where I want to end up, but I only have two drives right now.  Can I go ahead and start with just the two, and easily and the other two at a later date?  Or would I be better off waiting until I can get the other two drives?

 

First: Listen to what James says.

 

Some Netgear NAS users were a bit unlucky because they used RAID5 with BTRFS.

They lost all their data, because they did not know that RAID5 on BTRFS were not yet stable (See BTRFS status).

This really has nothing to do with whether RAID is a good idea or not, but it means that you need to know what you're doing and what you're working with, so you avoid losing data that you don't want to lose.

Just to clarify: It does not mean that BTRFS should be avoided or blamed. On the contrary, I'd use BTRFS where I can, because it's very fast and very well designed - in fact, it's probably the only real modern file system in existence.

(Personally I think Netgear were to blame, because they didn't investigate the status of BTRFS first, so they could either warn their customers or just disable the feature in their NAS).

 

That said, I love high data speeds. I don't mind having 40 drives in RAID0 configuration for things like compiling and video editing, just as long as my data lines are saturated. ;)

 

For my own examples, I'd rather pick a RAID0 using several 1TB 2.5" drives for fast temporary files and then when I'm done with the files, move them to a couple of backup disk (you easily get 10TB drives today; even 12TB SATA drives are available in many computer stores).

 

Backups are much more important than anything else. Once you've lost your web-directory (which contains *ALL* your Web-sites), it takes many years getting things back to something that resembles what they were. How do I know this ? -Well... I tried exactly that. The web directory disappeared without warning (on a Mac Mini). It was gone quicker than any RM command would remove it, so we're speaking milliseconds or microseconds and quickly the big bad syslog starts overwriting things.

-So ... Back up your data; set up an automatic backup somehow - free or commercial.

Another example is that one of my brother's friends got all his family photos on a damaged 2TB drive. it will cost a fortune to get the pictures recovered using a recovery service (around $2000). This was actually his backup drive. He decided to reformat his drive on his workstation and then copy back the files from the backup drive, just to find out that the backup harddisk was dead.

Of course, he could reconstruct the data manually, pixel-by-pixel. I don't know exactly how long that would take, but I think it wouldn't beat the time it takes to put aside some extra money for a second backup disk and copy the files over before reformatting the workstation drive.

-So ... Back up your backups too. ;)

 

I'm pretty sure that you know which path to take. After all, no one but you know the level of importance your files have.

 

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On January 30, 2018 at 6:22 PM, LarryM said:

Got notice that my Helios 4 is on it's way.  Yay!  But I have a question that I don't see here.  I followed the topic of creating, I believe it was a raid 10 with four disks, and I think that's where I want to end up, but I only have two drives right now.  Can I go ahead and start with just the two, and easily and the other two at a later date?  Or would I be better off waiting until I can get the other two drives?

-And to answer your question ... :)

 

It would really be easiest for you to wait until you've got all the drives you need.

 

RAID1 requires a minimum of two drives.

RAID0 requires a minimum of two drives.

RAID10 requires a minimum of 4 drives.

 

Imagine you configure your drives as RAID0, then you want to add a third drive; you'll have to erase all the data on your existing RAID0, when you add the third drive.

On the other hand, if you have two drives in RAID0 and you get two more drives at the same time later on, then you might be lucky enough to be able to mirror those first two drives onto the new two drives and set up a mirror on top of those, but that's really not a good configuration.

 

If you configure your drives as RAID1 (mirrored), then you'd also have to mess around with things when you get two more drives.

 

It's not just a matter of duplicating the drive contents (because some sectors contain control information that identify the RAID member).
-You'd have to have a RAID utility that does the work for you, so check the utility you're going to create the RAID with and see if it's capable of expanding an existing configuration.

 

Doing the above without having a backup of your data is not a good idea, because the word 'woops' in this context means that you've lost all your data in one go.

 

As James indirectly said: You could also start in a RAID1 configuration, then when you get the next two drives, purchase a 8TB drive or 10TB drive, back up all your data to that drive and reconfigure your RAID, then copy the data back.

 

Note: For backup drives, it's quite convenient to purchase a USB3 harddisk docking station, they're quite affordable and speed is fair.

 

 

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