Drive configuration puzzle

[sqwob]

Hi,

I've been following these forums the past few weeks and reading up on the documentation quite a bit, but still haven't figured out how i'm going to configure my hard drives / Volumes in my upcoming (first) FreeNas build.

Current situation:

• I have a running Thecus 4200 ECO with 4 2tb disks in RAID5, containing about 4TB of data
• I have a new build almost ready (Pentium G860 3Ghz - 8gb RAM & 4 additional 2TB disks)

My goal is to have a system with all 8 2tb disks in the final system, and all data migrated. I don't have any (significant) drives to temporarily store my data.
I understand that:
A) 4 disk raid5 or 4 disk RaidZ1 configurations are not recommended
B) an 8 disk raidz2 config would be a very good situation, but i doubt that i can reach that configuration without having temporary data storage?
C) I shouldn't expect issues mixing different brand drives, as long as i use 4k blocks for all
D) UFS would most likely outperform ZFS in my case, since i only have 8gb of ram (this is for domestic, single user use)

All feedback is appreciated

Kind regards,
Rik

 

[William Grzybowski]

4 disk raidz1 is not optimal but as you said, it is for domestic usage so I don't think you're getting any problems with that, you'll probably be network bounded.
So what I would do is create a 4 disk raidz in your new build, move data from old, move old disks to new build and expand the volume with those 4 disks, getting a 2x4 raidz volume/pool

 

[sqwob]

A related question: would the configuration William describes perform as good as one of the 4-disk arrays, or get better performance because there are 2 x 4disk arrays in the pool? (in other words does freenas combine the two arrays in a way that improves performance or shouldn't I expect this?)

I can read here: http://doc.freenas.org/index.php/Volumes#Volume_Manager

to extend a three drive RAIDZ1, add three additional drives. The result is a RAIDZ+0, similar to RAID 50 on a hardware controller.

- So I can assume that this would give me a significant perfomance increase for large files right (compared to the 4 disk array)?
- How would this perform compared to a Z2 over 8 disks?

or is the perfmance bottlenecked by the single gigabit network card anyway?

 

[William Grzybowski]

The performance would be increased, higher IOPS, however as in his case the first vdev will be full before adding the second the old files will not be splited across vdevs.

It would be faster compared to z2 of 8 disks, but the perfmance bottlenecked by the single gigabit network in any case.

Those days a single disk can almost saturate gigabit.

 

[sqwob]

Strange concept of having old data on one vdev, and the newer data on both vdevs as long as long as there is room on the first... and i assume there is no way (or reason) to redistribute the existing files over all disks after I add the second array?

I found this post from 2010 but maybe things have changed in the time being?

Quote:

Is there some sort of script that will re-distribute the data, preferably at a scheduled time (like 4 AM - 6 AM every morning) until it's finished?

Not at the ZFS level. But you could copy all data to a new directory/filesystem, duplicating all data. That would require enough free space. Such things can be done on the command line, jobs can control whether to pause or resume this job.

 

[William Grzybowski]

No, only way would be rewrite all, but I don't think it is worth it.

 

[sqwob]

Great, thanks for the feedback!

By the way, should I be able to achieve a similar result using UFS instead of ZFS?

 

[William Grzybowski]

No, FreeNAS does not support raid5/raid6 in UFS, just raid3 which I don't recommend and wouldn't really fit in your case.

 

[sqwob]

guess i'll better be looking into a ups then... any cheap recommendations (something that'll just get the server shutdowned when power fails)

Would this suffice: APC Back-UPS ES 550VA 230V ?

 

[William Grzybowski]

It's always good to have an UPS but I didn't really see the connection you made with zfs + ups.

 

[sqwob]

I was under the impression that one of the key properties of ZFS / Freenas was that it uses all available memory, and that you have an increased chance of dataloss when a system improperly shuts down?

 

[William Grzybowski]

Well, there is a slight chance that you lose data of an uncommitted transaction, which is defaulted to 5 seconds. I personally would not worry about it.

 

[sqwob]

Thank you very much for your time!