4tb drives x 8 or 10 with raidz2?

[Jay3443]

Which would be better to maximize space?

thanks

 

[DrKK]

Are you asking which has more space: 8 drives, or 10 drives?

Take a guess.

I assume you made a mistake in your question.

 

[Jay3443]

Are you asking which has more space: 8 drives, or 10 drives?

Take a guess.

I assume you made a mistake in your question.

Im just looking for an optimum configuration, I was reading where so many drives would mean wasted space etc, unless you go with 6x3tb would be optimal, 8x3tb i read somewhere would waste a terrabyte of space because not optimal. My question was, would it be a good idea to go with an 8 drive system, or would i be wasting space because it isnt optimal for raidz2. Or would it be more OPTIMAL to go with 10 drives, or would it be more OPTIMAL to go with just 6?

 

[HoneyBadger]

RAIDZ2 in any configuration will yield a total of (drives - 2) x (size of drives) - there's no "wasted space" that is lost based on drive count. You will "lose space" based on converting TB (what your drive is sold as) to TiB (what your bytes are allocated as). Multiply your unformatted space by 0.909 to get an approximation of that.

So 6x3TB = (6-2)x3 = 12TB unformatted, or ~10.9TiB formatted.

 

[Jay3443]

RAIDZ2 in any configuration will yield a total of (drives - 2) x (size of drives) - there's no "wasted space" that is lost based on drive count. You will "lose space" based on converting TB (what your drive is sold as) to TiB (what your bytes are allocated as). Multiply your unformatted space by 0.909 to get an approximation of that.

So 6x3TB = (6-2)x3 = 12TB unformatted, or ~10.9TiB formatted.

Thanks, I thought there was an issue with space being wasted in non optimal setups. I think

RAIDZ2 in any configuration will yield a total of (drives - 2) x (size of drives) - there's no "wasted space" that is lost based on drive count. You will "lose space" based on converting TB (what your drive is sold as) to TiB (what your bytes are allocated as). Multiply your unformatted space by 0.909 to get an approximation of that.

So 6x3TB = (6-2)x3 = 12TB unformatted, or ~10.9TiB formatted.

Thanks, I set up a test system on virtual box with 4gig virtual drives, freenas says 6 and 10 are optimal, not 8. So I was wondering what if its a performance or space hit im taking for going with 8 drives.

 

[DrKK]

Thanks, I thought there was an issue with space being wasted in non optimal setups. I think

There is a slight/theoretical loss of optimal pool performance for certain numbers of drives in certain RAID configurations, but, generally speaking, for Joe Blow home user, these are not particularly worth considering. Perhaps that is what you read.

 

[Jay3443]

There is a slight/theoretical loss of optimal pool performance for certain numbers of drives in certain RAID configurations, but, generally speaking, for Joe Blow home user, these are not particularly worth considering. Perhaps that is what you read.

Heres the link that says ill "waste" 1.149 - 0.26 TB of space (~1TB) by choosing 8 disks over 6. This is with 3TB disks.
But would it be the same for 4tb disks?

https://forums.freenas.org/index.php?threads/raidz2-number-of-disks.16153/

 

[HardChargin]

@Jay3443 I can tell you that I built a raidz2 pool with 8 4TB drives, was expecting approximately 21TiB available, and ended up with closer to 20TiB available. Not accounting for the 80% of total available pool space usage rule which amounts to about 16TiB usable space.

Performance is a non-issue for me. I used 7200rpm drives and easily saturate my 1Gb network.

 

[jgreco]

mod note: moved to New User Forum

 

[SirMaster]

RAIDZ2 in any configuration will yield a total of (drives - 2) x (size of drives) - there's no "wasted space" that is lost based on drive count. You will "lose space" based on converting TB (what your drive is sold as) to TiB (what your bytes are allocated as). Multiply your unformatted space by 0.909 to get an approximation of that.

So 6x3TB = (6-2)x3 = 12TB unformatted, or ~10.9TiB formatted.

There actually can be a waste of space if you use ashift=12 (which most people with modern consumer disks should be using).

See this with detail: https://web.archive.org/web/2014040...s.org/ritk/zfs-4k-aligned-space-overhead.html

For example, with 12x4TB RAIDZ2 there is a waste of 2.91TiB due to alignment padding and allocation overhead.


Though I should also note that there are ways to deal with this. For example, if you change the recordsize on your datasets (from the default 128KiB) to 1 MiB and you make sure to have compression enabled. Then you can avoid pretty much all of this alignment padding and allocation overhead.

But if you stick with 128 KiB blocks and ashift=12 then you will always have some amount of wasted space unless you are using 6-disks or 18 disks in your RAIDZ2. with 6 and 18 disks the alignment padding and allocation overhead are zero and the only overhead comes from the reserved space for metadata which will always, alawys be there.

I should also note that adding another disk to your vdev will always increase your space. You never lose space by adding a disk, but for some number of disks in your vdev you don't gain as much by adding 1 more disk as you do with other numbers of disks in your vdev.

 

[Jay3443]

Thanks for all the info, Im still trying to decide, but leaning towards going with just the 8 drives, these are wd green drives so going with 10 would just mean more drives possibly to fail. Plus my server only has 4 gigs of ram.

 

[HoneyBadger]

these are wd green drives

You should change that as WD Greens are awful. If you have no other choice or already own the drives then make sure you "fix them" with wdidle:

https://forums.freenas.org/index.php?threads/hacking-wd-greens-and-reds-with-wdidle3-exe.18171/

Plus my server only has 4 gigs of ram

You should really change that as 8GB of RAM is the minimum recommended spec for 9.2 and later.

 

[Jay3443]

You should change that as WD Greens are awful. If you have no other choice or already own the drives then make sure you "fix them" with wdidle:

https://forums.freenas.org/index.php?threads/hacking-wd-greens-and-reds-with-wdidle3-exe.18171/



You should really change that as 8GB of RAM is the minimum recommended spec for 9.2 and later.

I know I should upgrade but ive been running 9.2. on my main server and a backup server for a couple years now with no problems, so im just gona upgrade to 9.2.1.9 and keep going. My next server will have at least a i5 with plenty of ram and 10 drives.

 

[Darren Myers]

I don't think i would plan any harddrive upgrades until i upgraded my server hardware itself....i would deff want 16+ Gb of RAM before i go about buying/adding harddrives or any size.

 

[Jay3443]

Lol, more to consider, just as I was getting ready to build the pool. Ok, Ill look up my motherboard specs and order some ram from ebay before I start. Hopefully these dual core e8500's support 16g ram.

 

[Darren Myers]

Lol, more to consider, just as I was getting ready to build the pool. Ok, Ill look up my motherboard specs and order some ram from ebay before I start. Hopefully these dual core e8500's support 16g ram.

full system specs are usually helpful for us in general, so we know how many SAS/SATA ports you have etc.

 

[HoneyBadger]

There's also no i5's with ECC support (edit: other than the i5-4570TE and a bunch of BGA mobile parts)

 

[jgreco]

You should really change that as 8GB of RAM is the minimum recommended spec for 9.2 and later.

I bumped that up to 8GB long before FreeNAS 9.

 

[ewhac]

There's also no i5's with ECC support.

Um...

There's no fifth-gens, but there are a handful of fourth-gens...

 

[HoneyBadger]

I bumped that up to 8GB long before FreeNAS 9.

Could have sworn I saw 4GB as the minimum back on the 9.1 branch, but looking at the old docs I see 6GB as far back as 8.0.1