growing redundant storage

[mattmac24]

Hi Guys,

Ive just bought a HP N54L Microserver and will be using it for storing all my media as well as a time machine backup server. Currently I have a single WD Green 3TB USB drive that ive filled, the NAS will be replacing this and doing a lot more. I only want to buy 2 new drives at the moment (WD 3TB Red) for the NAS and copy my existing data across and then use the old 3TB USB as a general portable hard drive(I cant imagine mixing Green and Red drives is good anyway).

I would like to know if it is possible or not to only buy 2 drives now and then grow the array later down the track(keeping data intact) whilst always only keeping one drive as a parity. With constantly falling hard drive prices I would rather only buy the drives as I need them. Im unfamiliar with ZFS which now seems to be what FreeNAS is all about, last time i setup a FreeNAS a few years back it was using RAID5, so i would either be using RAID5 again or the ZFS equivalent. the N54L only comes with 2GB of RAM so if im going with the ZFS option i will need to bump the ram up to 8 or 16 GB.

Ideally my setup would be:
Now - 2x3TB with 3TB usable
Down the track - 3x3TB with 6TB usable
Further down the track - 4x3TB with 9TB usable

Thanks!

 

[toddos]

You can't setup RAID-Z1 with only two drives, so your first 2x3TB would be mirroring. You can't change from mirroring to RAID-Z1, so you can't go from 2x3TB mirrored to 3x3TB RAID-Z1 on the fly. And you can't add disks to an existing RAID-Z1, so you can't go from 3x3TB to 4x3TB, either.

What you can do is add drives to your pool in redundant chunks. So if you start off with 2x3TB mirrored, you can add another 2x3TB mirrored for a total of 4x3TB with 6TB usable (you can lose two drives, but only one from each mirror -- if you lose an entire set of 2x3TB drives, you lose everything). Or you could start with 2x3TB mirrored and add a 3x3TB Z1 for 5x3TB with 9TB usable (you can lose one drive from the mirror and one drive from the Z1, but if you lose two drives from the mirror or the Z1 you lose everything). And so on.

The GUI superficially will allow you to add drives the way you want, but it's not going to do what you want it to do and what you're really doing is adding non-redundant sets. So in your example, you start with 2x3TB mirrored and you add one drive. You don't end up with 3x3TB Z1, but 2x3TB mirrored + 1x3TB "striped" (no redundancy). And then when you add your 4th drive, you don't end up with 4x3TB Z1, but 2x3TB mirrored + 1x3TB + 1x3TB. In both scenarios, if you lose any of the 1x3TB drives, you lose everything. And before you say, "That'll never happen to me," there's a guy who just had that happen because he added non-redundant drives. And now he's looking at $2,000+ to try to recover an image of the dead drive so he can put it on a new drive to recover his pool, so that he can recover at least some of his data. And that's nowhere near the first time someone's posted here with the exact same problem. Don't be that guy.

Edit: The N54L maxes out at 8GB of RAM. So that's something to think about. ZFS likes to have 1GB of RAM per 1TB of storage space available, so if you see yourself ever going over 8TB, the N54L won't be able to keep up with RAM.

 

[ProtoSD]

Also, read this Sticky post in the Noob section:

http://forums.freenas.org/showthread.php?7775-Slideshow-explaining-VDev-zpool-ZIL-and-L2ARC-for-noobs!

 

[gpsguy]

Some people have been successful using the N54L with 16Gb ECC ram.

The N54L maxes out at 8GB of RAM.

 

[mattmac24]

Thanks for the responses guys, i've had a read through that power point presentation and now I have a solution set out in my head at least. I dont need any double redundancy and I cant really justify the cost/loss of usable storage

Im going to be upgrading to 16GB of ram soon enough. For the moment im going to buy 2x3TB drives and set them up as a RAID1. Then when i want to buy another drive to add in I will buy a 4TB hard drive as well, backup the data to it, create the 3x3TB RAIDZ1, copy the data back from the 4TB USB drive and then return the 4TB drive the next day :p

Also going to run CouchPotato, SickBeard and sabnzbd on my new FreeNAS and Plex Media Server on an old Laptop which should handle the transcoding :)

 

[cyberjock]

I'll just warn you that the double parity is almost a necessity unless you have religious backups. If a disk fails and any other disk has even a single bad sector you will have some data loss. The statistical probability of a single bad sector is becoming a major problem because of the large disk sizes available. RAID5(and RAIDZ1) was considered "dead" back in 2009 or so because of the almost guaranteed bad sector. Quite a few people in recent weeks have had data loss because the had only 1 disk redundancy.

 

[mattmac24]

I'll just warn you that the double parity is almost a necessity unless you have religious backups. If a disk fails and any other disk has even a single bad sector you will have some data loss. The statistical probability of a single bad sector is becoming a major problem because of the large disk sizes available. RAID5(and RAIDZ1) was considered "dead" back in 2009 or so because of the almost guaranteed bad sector. Quite a few people in recent weeks have had data loss because the had only 1 disk redundancy.

Interesting, but in that I'm mainly going to be storing movies and TV shows would my whole array be shot or just the movie that was unlucky enough to be stored on a bad sector? How do i check for dead sectors? None of the data is critical, its just media. In an ideal world I would have a second NAS in a fireproof safe somewhere mirroring this NAS, but thats just cost prohibitive so im willing to accept that my data is not indestructible.

 

[cyberjock]

Scrubs can find bad sectors that are being used. Long SMART test are supposed to find bad sectors that are unused, but that's no guarantee for some models and brands. Also keep in mind that just because you didn't find one last scrub/SMART test doesn't mean it won't appear now. The problem is with the statistical chances of one being bad that wasn't before.. so you're already working against the odds. :P

Depending on what the sector is storing it can be a single file, a single folder, or the whole zpool. Of course it's far more likely to be a single file, but people have lost their whole pool because the file system was corrupted.

Personally, I would never build a FreeNAS server in a production environment without dual redundancy(especially if you don't have religious backups).