RAID Z2 Questions

[Mike Bruns]

Merry Christmas and Happy Holidays!

First of all, I think this should be required reading for everyone new to Freenas and storage systems in general.

https://forums.freenas.org/index.php?threads/help-recover-my-data-please-freaking-out.35011/​

Not that Freenas is bad or dangerous (quite the opposite), just that if you cut corners or don't know what you're doing, could could put yourself in a world of hurt. It convinced me to go from RAIDZ1 to RAIDZ2, and from non-ECC RAM to ECC RAM. You can buy 16GB ECC RAM from Amazon for under $100. Anyway, I have 2 questions:

1) I'd like to go with a 5-disk x 6TB - RAIDZ2 setup. I've seen mixed answers as to storage overhead going with 5 disks rather than 6 I.E (p^2)+2 Is the storage overhead significant? I'm not worried about perforamce overhead, as I'm sure I'll saturate my gigabit LAN long before I'll hit the limits of my server and disks.

2) My server is a Dell Poweredge 110 ii. Are there any downsides to putting the fifth 3.5" drive in the 5.25" empty tape slot with a 5.25"->3.5" adapter? In initial testing, Freenas picks up the drive just fine and I don't see any speed differences with the SATA cables that were connected to the CD drive.

 

[nightshade00013]

As far as data transfer this https://calomel.org/zfs_raid_speed_capacity.html will give you an good guestimate of the speed you will get from your disks. If you use 5400RPM drives it will be a bit less by around 15 to 20 percent as the test used 7200RPM drives.

It won't matter too much about 5 vs 6 disks it's just that 6 is a little more idea for everything and gives you more space for storage since 2 disks worth will be parity. You can do a 4 disk RaidZ2 but will only have the capacity of 2 disks minus overhead.

Using a 5.25 inch slot is fine just make sure it has good airflow like the rest of the drives should have. An empty slot is an empty slot and will do the same job as a larger one with an adapter to make sure the drive is secured correctly. It may work even better since you will have more air space and the adapter will act like a mini heatsink.

 

[depasseg]

First of all, I think this should be required reading for everyone new to Freenas and storage systems in general.
https://forums.freenas.org/index.php?threads/help-recover-my-data-please-freaking-out.35011/

Great idea!

1) I'd like to go with a 5-disk x 6TB - RAIDZ2 setup. I've seen mixed answers as to storage overhead going with 5 disks rather than 6 I.E (p^2)+2 Is the storage overhead significant? I'm not worried about perforamce overhead, as I'm sure I'll saturate my gigabit LAN long before I'll hit the limits of my server and disks.

Assuming you are taking about ZFS file system overhead, @Bidule0hm has a great calculator. Check it out and compare the Z1 and Z2 data.

2) My server is a Dell Poweredge 110 ii. Are there any downsides to putting the fifth 3.5" drive in the 5.25" empty tape slot with a 5.25"->3.5" adapter? In initial testing, Freenas picks up the drive just fine and I don't see any speed differences with the SATA cables that were connected to the CD drive.

I don't see any issue with this. A single drive is no where close to being able to saturate a SATA link, so I wouldn't worry about it.

 

[Mike Bruns]

Thanks all, I'm currently running just fine with the 5 disk RAIDZ2 setup.

I've almost convinced myself to add an additional disk now, before I lock down the server and start migrating data. I'll never use the CD-ROM and can use that slot for the 6th drive. But the Dell Poweredge T110 motherboard only has 5 SATA ports. 4 normal SATA + the optical. I'd need to add a PCI SATA card for the drive.

Are there other benefits I'd get adding the LSI (or IBM 1015) card rather than using the motherboard SATA ports? From what I can tell, it's another $150 for the card and cables.

 

[nightshade00013]

Benefits to adding the card, for you not likely unless you upgrade to SAS drives and spend a whole lot more money. There would be an advantage if you had a case with more expansion capability but from what I can tell you will just be throwing money at a problem that does not exist. Even extremely fast hard drives can not max out sata connections.

If you have 5 drives and no extra sata ports I wouldn't worry about it. Use what you have and continue on. Just remember to get a case with more expansion ability on the next build.

 

[Scharbag]

One thing that sucks with ZFS is you cannot add a drive to a vdev. You can add another vdev to a pool. Vdevs can be different but it is recommended to stay consistent. That said, you will need to decide if you want to upgrade using you first case with an external JBOD chassis or if you will migrate to a new case. IF you have 5 disk vdevs, then your next upgrade will need 10 drive capacity. 6 will need 12 etc.

As for the SAS card, it is awesome for expandability if you think you will go that route. You will also need a SAS expander (Intel or HP make good ones, see my sig for Intel) to connect to more than 8 drives (9211-8i type cards can directly connect to 8 drives with 2 sets of breakout cables).

I use a 20 bay hot swap case and I have 22 drives plus a CD/DVD reader in it. I love it. Allows me to have a big Z2 production pool and a nice sized Z1 backup pool. With the expander and SAS cards, I can easily hook a 24 drive JBOD chassis to the server and expand in groups of 6 disks for both pools. I may have OCD...

Cheers,

 

[Mike Bruns]

I'm going to stay with my current config for now, 15TB should be enough (famous last words). If I run low, I'll deal with it separately.

Like many things, this build changed as I went. A month ago, I had never heard of FreeNAS, I just found a fantastic deal on a Dell Poweredge server on black-friday and didn't know what I was going to do with it. The new setup (Dell T110, 16GB Ram, 5x6TB Drives, Raidz2) gives me a far more reliable file and backup-server.

I own a 10-person company, and while I had done a "decent" job of backing up my critical data, there were just too many single points of failure that could have caused a long recovery/outage or lost up to a week of data. After I copy the data from the old smaller harddrives to the new NAS, it's amazing how many are failing smartctl tests.

This is also giving me a good opportunity to download, compare, and truly test my cloud offsite backups to make sure I can restore properly. A DBA once told me, "A backup without a tested restore is just hope".

 

[Scharbag]

"A DBA once told me, "A backup without a tested restore is just hope".

Words to live by.