Add a 4th disk

[WhiteTiger]

I newbie with FreeNAS.

I've assembled a little NAS with 4 disk thinking a RAIDZ pool, but during the installation I've seen that a disk is defective.
So I wish to install only 3 disks and to save the data; then to add the 4th disk when it'll arrive.
Is this possible or I'll have to remove the pool (and to lose the data) ?

Thanks in advance

 

[gpsguy]

No, it's not possible. You'd need to destroy the pool and start over.

With today's big disk capacities, RAIDz2 is a better option.

 

[WhiteTiger]

OK, I'll wait, but I perplexed about this.

For my need there are no problem, I'll wait; but I wanted to propose FreeNAS in my office.
Here we are thinking about a system with many more disks, starting with only 4 and then add the others only when it is need.
But we cannot destroy the pool every time.
Is there another solution?

 

[joeschmuck]

You would add a group of drives, not a single drive to expand your system. To be honest, you are better off if you have an idea about how much storage space you need and to double it, then install that amount in a RAIDZ2 configuration at a minimum. Here is a link to a RAID calculator. Use it to see what configuration gives you the correct usable space you will need.

What is the purpose of your FreeNAS system? Backups, active use files and databases? I ask because you need to know this up front before purchasing any components. If you don't' know what you will be doing with it, then you don't know what to buy without wasting your money. For instance, will you only be doing backups? If so then you don't need a fast system. If you are going to host files for the office to use, how many people will be using the server at one time? Will you need fast hard drives or will slow drives be fine? You might want a mixture of drive types as well, fast ones for live data and slow ones for backups to save some money. Do you need encrypted drives? That means you need to correct CPU for fast operations.

I'm just trying to be helpful here by pointing out things you must be thinking of before purchasing anything. And a business use items means there are likely risks that you don't want to take. Do a risk assessment, it will help.

 

[cyberjock]

Check out my noobie presentation(link in my sig) That would have answered your question for you with very friendly visual aids. :)

 

[WhiteTiger]

Thank you for your reply Joeshmuck.

My project is oriented to a SME company or a little department, so a little number of users: from 20 to 100 users.
In my company there are 5 departments with an average of 30 users.
I think about two system: a NAS for storage the files and a system for backup of this.

For example, NAS in the departments and Backup system in one or two different point at the corporate level.

In the first context I think about a system with 4 - 15 disk slots.
Initially I was thinking to start with only 4 disks for RAID 5, now I'm reading about RAIDZ and RAIDZ2.
In a department I can install disks of 1,5TB, in another department disks of 3TB.
With a backup activated I think I can accept the risk of having a second failure while I'm waiting for the replacement of the first disk failed.

So, the point is not this, but if is possible to expand the storage area.
If today I install a "real" storage space about 4,5 TB, I cannot think to destroy it next year only to add others one or two disks.

In this server I was thinking a some "backup" function to "copy" files to another system.
Which model of system and how much space for this is my nightmare.
With several TB of space I can no longer think of a model like the old Grand father - Father - Sons because I should have an area equal to 8 or 10 times the space used.
So any suggestion is welcome.

 

[joeschmuck]

Simple answer is yes, you can expand the storage without needing to destroy your pool however if you look at Cyberjocks guide for how ZFS RAIDs work, you can figure it out. For example lets say you start with six 2TB drives, this gives you about 9TB of storage space in a RAIDZ2 configuration. If you wanted to expand this later to say double the storage the storage with another six hard drives and add them to your pool. There is a specific way to do this and if you get it wrong then you could loose all your data with the loss of a single drive addition. I'm not the expert, Cyberjock is and there are many others here who know what they are talking about.

With 20 to 100 users then you need to be thinking about enterprise class hard drives and probably an HBA controller card.

As for waiting for a replacement hard drive, in a work environment I would have a spare sitting in a cabinet read for when a drive does fail. It will happen and the more drives you add, the more you will see drives failing. Where I work the IT folks are replacing one to two drives a day. We have about 5000 employees so it's quite a large server room.

As for Grand father - Father - Son backups, that is where snapshots come in. I'm not expert there either but I do know they can consume a lot of space. It my work place the snapshots are taken every 24 hours on the majority of the servers and retained for several months (depends on the server). I have no idea of the frequency of the financial servers but I could see that occurring more frequently since money is very vital.

Whatever you plan on doing, sit down and write it out. Bounce it off someone. I know if you know your requirement that if you PM Cyberjock, for a fee he will give you some of the best guidance you can get. Send him a PM, your money will be well spent.

 

[ZFS Noob]

So, the point is not this, but if is possible to expand the storage area.
If today I install a "real" storage space about 4,5 TB, I cannot think to destroy it next year only to add others one or two disks.

I'll only address the part of this that it seems like you don't understand.

There are two components you need to wrap your head around when thinking about RAID:

1. vdev: this is a virtual device made up of one or more actual disks. These can be single, or mirrored (including things like 3-way mirrors), or set up on a parity RAID configuration like RAIDZ2. Once a parity raid vdev has been created it can not be expanded.
2. Zpool: this is a stripe of vdevs. The Zpool doesn't care about the nature of the underlying vdev, and it will let you stripe across a RAIDZ3 vdev, and a mirrored vdev, and a single drive vdev. However, as this is a stripe, if any vdev fails the pool is lost.

If you create a RAIDZ(whatever) vdev on FreeNAS, then you can not add additional drives to it later and expand it as you can with higher-end RAID controllers. A 5 drive RAIDZ3 vedv will alwaysbe a 5 drive RAIDZ3 vdev. If you want to add more drives, then you need to create another vdev and add it to the pool, which then stripes across both vdevs (and generates some performance gains as part of the process.)
So, what you can do instead is create 2 mirrored vdevs, and add them to a pool so they're striped together, and as you decide to add more data later you can just add more mirrored vdevs, so you'll be adding two drives at a time. Again, though, this is different than what you're used to with RAID cards:

• The Zpool stripes across all the vdevs in the pool, but it does so proportionally based on their available capacity.
• The Zpool's data is not evenly distributed across the entire pool when the pool is expanded. If you've got a Zpool made up of one mirrored vdev at 90% capacity and you add a new vdev to the pool that's otherwise identical, now you have a pool consisting of one vdev @ 90% capacity, and one at 0% capacity. Writes will favor the new vdev at 9:1 or so, and you won't see the doubling of read/write performance that you would otherwise expect in a stripe.

So there's a lot to get you head around -- even if you've been doing this for a while, it isn't what you're used to.
If you want to add drives over time, ignore RAIDZ1 (because it's bad form to use it with big drives - this will cause data loss when resilvering just like with RAID5 does in the 1TB drive world), and choose one of the following:

• Add mirrors, and grow the thing using mirrors. If initial performance is fine you won't lose anything, but if you need additional IOPS in addition to additional capacity you'll need to move the contents off the Zpool then back on it.
• Start with a RAIDZ2 vdev of an appropriate number of drives (<= 8, but search is your friend), and when it's time to bump capacity add another RAIDZ2 vdev. Again, you won't see performance gains unless you migrate the data off and back on again.
• Build what you want now, with the understanding that you'll need to destroy the Zpool and create a larger one when you need to expand it. Plan to do this on a weekend when you won't affect the business.

Something else you probably also don't understand. RAID6 has read performance equal to (the number of drives in the array minus 2) * the performance of an individual drive. RAIDZ2 (the ZFS alternative) has performance ~= to the speed of one drive. So if you build a 100 drive RAIDZ2 vdev (not recommended), it will be about as fast as a single drive. ZFS does this to guarantee data integrity by protecting against some kind of faults, but if you're not expecting it you'll look like an idiot when you don't get the performance you planned for.
As always, I'm a n00b here, but I hope this helped.

 

[WhiteTiger]

Check out my noobie presentation(link in my sig) That would have answered your question for you with very friendly visual aids. :)

I have read your guide. Congratulations!
I realized two things: how to expand storage and that however my hardware is not good because it allows only 4 disks. :(