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What is the best setup for an zpool intended for database big inserts or TCP/IP dumps (i mean sustained high write throughput using 4 disks ?

I want buy 4 Wd RE4 2TB drives and get the more power i can !

i think of

zpool create tank mirror disk1 disk2 disk3 disk4

OR

zpool create tank mirror disk1 disk2 mirror disk3 disk4

OR

zpool create tank disk1 disk2 disk3 disk4

i think the solution with two mirror in a pool is the best, but not sure.

edit : ok so mirror IS RAID1. It is not possible to make this setup : RAID0 (RAID0, RAID0)

Avlin
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3 Answers3

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The three commands and ZFS setups you've listed are vastly different configurations.

zpool create tank mirror disk1 disk2 disk3 disk4

This creates a 4-way mirror with the capacity of ONE disk. Lots of protection, less space and less performance.
I don't think you want that.

zpool create tank mirror disk1 disk2 mirror disk3 disk4

This creates a stripe of two RAID 1 mirrors - RAID 1+0, with a capacity of TWO disks.
This is a good balance.

zpool create tank disk1 disk2 disk3 disk4

This creates a stripe of four disks - RAID 0, no protection against failure and a capacity of FOUR disks.
This is fast, but only make sense if you don't care about your data's integrity. If a drive fails, you will lose all of your data

twoleggedhorse
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ewwhite
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  • I best understand now. I thought it was possible to make raid0 of raid0 but mirror is RAID1 not RAID0 – Avlin Sep 24 '12 at 12:46
  • RAID0 (RAID0, RAID0) is the same as a three-way stripe... so `zpool create tank disk1 disk2 disk3 disk4` would be all RAID 0, and thus, the fastest. But there would not be any data protection. – ewwhite Sep 24 '12 at 12:59
  • OK Thanks. For me the best setup for programing/ research is two zpool: a 5400rpm raidz with l2arc ssd for all data and stripping with 10k disk no ssd l2arc for serious work. I mean the raidz pool can handle backup from the stripped pool. – Avlin Sep 24 '12 at 13:07
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Here's how mirror and striping work:

  • If you want more write throughput, then more stripes
  • If you want more fault tolerance and read performance, then more mirrors

So with 4 disks, the best way to achieve the most throughput without sacrificing fault tolerance is to create 2 mirrors, allowing the data to stripe over the mirrored pairs.

To take this further, if you had six disks, this configuration would give you more write performance:

zpool create tank mirror disk1 disk2 mirror disk3 disk4 mirror disk5 disk6

And this would give you more fault tolerance:

zpool create tank mirror disk1 disk2 disk3 mirror disk4 disk5 disk6
longneck
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As I understand you'll do massive writes (vs a lot of small random writes), raidz might be a good space/redundancy compromise:

zpool create tank raidz disk1 disk2 disk3 disk4

Capacity of three disks, survives one disk failure.

jlliagre
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  • yeah, i have already a raidz of 5 1Tb caviar green but write IOPS seems not sufficient (for me). And you are limited with record size, expecialy on raidz and 4k drives. – Avlin Sep 24 '12 at 13:38
  • @Avlin Side note: RAIDz is RAM hungry, you'll get marginal performance unless you throw gigs of RAM at it. The processor has to be decent as well... – Chris S Sep 24 '12 at 14:06
  • That's it : raidz for movies and backup, zpool stripping and mirroring for databases and VMs. – Avlin Sep 24 '12 at 14:38
  • I understood the question to be about throughput (a small number of big writes) while if the goal is iops (a large number of small writes), raidz is indeed not optimal. – jlliagre Sep 24 '12 at 16:08