ZPool Config advice and Napp-IT Smart Test Errors

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K D

Well-Known Member
Dec 24, 2016
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I finally finished taking redundant backups of my main array and used it to create a new zpool with 4x (3drive Raidz) vdevs. A 400GB S3700 will be added as a SLOG device (Waiting for it to be delivered).

1. This array will be used for NFS and iSCSi data stores for esxi as well as media storage. I considered 6 mirrors but did not want to lose that extra 3 drives worth of storage for redundancy. I'm aware of the risk of losing 2 drives in the same VDEV and losing the entire pool and that is an acceptable risk. Is this an optimal way to use 12 drives from a performance standpoint? It will eventually be used over 10GBe.

2. I created the zpool in FreeNAS and imported it into Napp-IT. When I ran the smart check in napp-it, this is what I get. What does S:0 H:0 T:0 in the errors column mean?

2017-05-02 13_55_54-napp-it-san __ ZFS appliance.png
 

gea

Well-Known Member
Dec 31, 2010
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DE
1. mirror vs raid-z
The main difference is iops

If you count 150MB/s per disk sequentially and 100 iops per disk

on a mirror:
read: sequential and iops=2 x number of mirrors (as read is done in parallel) with
write:sequential and iops=1 x number of mirrors (as write must be done on bothl)

on a raid-z
read and write: sequential = n x number of datadisks, iops = n x number of vdevs

with 6 mirrors and around 150MB/s sequentially and say 100 iops per disk you can achieve
read: 12 x 150MB/s =1800 MB/s with 1200 iops
write: 6 x 150 MB/s = 900 MB/s with 600 iops

with 4 x raid-z of each 3 disks
read and write: 4 x 2 x 150 MB/s= 1200 MB/s with 400 iops

so sequential value is quite the same but iops is a huge difference.
On iops limited workloads (and ESXi or ZFS are mostly iops limited) there is a difference.
For a media server iops is not that relevant.

2. iostat errors
iostat errors are driver messages counted from bootup on. They can indicate (future) problems.
Real ZFS errors are detected due checksums with a drive offline/ pool degraded.
Iostat -E, whats that all about? (The dot in ... --- ...)
 
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