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List:       zfs-discuss
Subject:    Re: [zfs-discuss] Rule of Thumb for zfs server sizing with (192)
From:       William Papolis <wpapolis () gmail ! com>
Date:       2007-09-29 20:48:04
Message-ID: 27835995.1191124189957.JavaMail.Twebapp () oss-app1
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I checked this out at the Solaris internals link above, because I am also interested \
in the best setup for ZFS.

Assuming 500GB drives ...

It turns out that the most cost effective option (meaning the least "lost" drive \
space due to redundancy is to ...

1. Setup RaidZ of up to 8 drives (All must be the SAME size; 8 x 500GB)
2. Choose either 1 or 2 drives to be parity drives. (You lose this space)

Bottom line is ...
1. You have either 3.5TB or 3TB of space and (500 or 1TB for parity)
2. with 500GB or 1TB devoted for redundancy. (for parity)
3. You can simultaneously lose 1 or 2 drives and your ARRAY is still intact!

This maximizes space and performance should be up there too, right? 
How does this compare, performance wise, to 4 sets of 2-way mirrors?  (4 sets of 2 \
-way mirrors is the fastest setup right? But you lose half the available capacity!)

Thanks,

Bill

HERE IS THE QUOTE FROM SOLARIS INTERNALS FOR SIZING AN ARRAY

"RAID-Z Configuration Requirements and Recommendations

A RAID-Z configuration with N disks of size X with P parity disks can hold \
approximately (N-P)*X bytes and can withstand P device(s) failing before data \
integrity is compromised.

    * Start a single-parity RAID-Z (raidz) configuration at 3 disks (2+1)
    * Start a double-parity RAID-Z (raidz2) configuration at 5 disks (3+2)
    * (N+P) with P = 1 (raidz) or 2 (raidz2) and N equals 2, 4, or 8
    * The recommended number of disks per group is between 3 and 9. If you have more \
disks, use multiple groups. "  
 
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