# zfs speed: raidz vs mirror



## dbi (Apr 18, 2010)

Hi,

I want to have a ZFS only system.
I have 4 equal 500GB HDDs.

*Conditions:*
- I want to have at least 1TB free space. (e.g. one 4-way mirror isn't an option)
- The schema must be able to withstand at least 1 HDD failure (e.g. jbod/raid0 isn't an option)

*Goal:* Best speed possible

*Additional question:* Is it possible too boot from raidz?

My first thought was to use two mirrors, but I decided to ask first.

So, which schema that can withstand 1 hdd failure would produce best speed with 4 hdds?


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## vermaden (Apr 18, 2010)

> *Additional question:* Is it possible too boot from raidz?


You do not need to boot from ZFS, check that:
http://daemonforums.org/showthread.php?t=4200



> *Goal:* Best speed possible


Create RAID10 (RAID0 from two mirrors), RAID5 (raidz) does not increase performance, it just adds redudancy, you would have to create RAID50 to gain performance (RAID0 of two or more RAID5 arrays).

With RAID10 You will have 1TB space and two hard drives can fail without any problem, with decent performance.


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## Matty (Apr 18, 2010)

raid10 gives you almost twice the write performance and 4times the read performance. Even random reads have acceptable performance.


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## carlton_draught (Apr 22, 2010)

You might want to check out this post. (Lists the actual command to create a stripe of mirrors, as the others have suggested.) Good luck.

Do note that you can only withstand 2 drive failures if you happen to be lucky with which drives fail. If it's both drives from the one mirror, you're screwed. So: somewhat better fault tolerance than RAIDZ, but not as good as RAIDZ2 (which, for a 4 drive setup, will have the same storage capacity as the stripe of mirrors, not as fast, but can have ANY 2 drives fail without data loss).


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## wonslung (Apr 23, 2010)

also, it depends on what type of work load you have.  A lot of people keep saying raidz doesn't increase performance, but if you have a mostly sequential read oriented workload, it CAN.


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