RAID-Z: Too less Storage Capacity

[Spurgeon]

Hi.

Thanks for the great Open source product.

I'm evaluating FreeNAS 9.1 for implementation and have setup a VM (using virtual box) with 5 x 3 GB SATA HDDs. In reality, we'd use 3 TB Drives instead of GBs.

The ZFS volume using RAID-Z shows only 4 GB capacity against expected 10-11 GB shown by this RAID Calculator - http://www.servethehome.com/raid-calculator/

Is this a bug?

What would be actual (usable) storage capacity for 5 x 3 TB volume with RAID-Z?

Request your kind expert advice.

Thank you!
Regards
Spurgeon

 

[cyberjock]

This has been asked alot. 2GB per disk is assigned as swap space. So naturally you can expect a smaller pool. Actual disk usage for a RAIDZ1 would be about 3*4, or 12TB minus the conversion from base10 to base2, etc. That raid calculator doesn't apply to FreeNAS. We're better than everyone else(j/k).

Let me give you a few pointers since you're in the experimenting stage and I'm a little worried about you already:

1. VMs aren't recommended for production use and we typically see someone about once a week lose all of their data suddenly and without any warning or clue what is wrong. As a result one of our mods has written http://forums.freenas.org/threads/p...duction-as-a-virtual-machine.12484/#post58364 . If you are still hellbent on doing it anyway, the "safest" way is to follow http://forums.freenas.org/threads/a...ide-to-not-completely-losing-your-data.12714/ . Notice that I put safest in quotes because there's still considerable risk. And ignoring any one of those recommendations in the second thread is a pretty big red flag that you will have problems someday. As such, if you choose to virtualize you had better keep religious backups.
2. RAID1 isn't recommended because its not reliable in todays world of bigger disks. Read the link in my sig that I put there as words of warning from people that don't know how dangerous RAID5/RAIDZ1 is. Even then, we just had somoene 2 days ago lose signifcant amounts of data. Even now, he's not sure how much data he actually has left as he's still waiting for a zpool scrub to finish. Don't be a statistic. Go with RAIDZ2 and avoid UREs from killing your pool.
3. The manual and stickies in the forum are very well written and pretty thorough. If you read through all of the stickies in the various help&support sections of the forum and use the manual you can have a very reliable and trustworthy server. If not, you may end up very unhappy when you lose data. ZFS doesn't perform miracles, but it expects you to be informed on how it works and what decisions are smart and what aren't.

 

[Spurgeon]

Dear Cyberjock,

Thanks a ton for your kind, instant and invaluable inputs!

Yes! I fully agree with you on use of VM for production.

I was only evaluating FreeNAS for capacity / features / cost (i have a Core i3 2.8G / 8 GB / 5 x 3 TB HDD box in mind for this) against NAS enclosures.

We are looking for a NAS with about 12 - 20 TB capacity for video archival (mostly .mov and .mp3 stuff).

Thanks for the recommendations on RAID-Z1, sure, we'll dump it and consider Z2.

Once again, thanks a ton for your kind help and inputs!

warm regards & gratitude,
Spurgeon