# ZFS Mirror Vs GMirror



## Brokenby2703 (May 7, 2010)

Hello to everybody.
My first post here (although reading you daily since years).

I have an old DELL Power Edge Server PE 1800 as follow:
2 GB Ram
2x Sata I  80GB Hard Disk (on controller onboard)
2x Sata II 500GB Hard Disk (on controller pci-x sil.3124) 
Xeon 3.0 Ghz CPU
1x External Tape Unit (DLT) for nightly backup.

I would like to use this old server as NAS unit for our office with the following configuration.

The 2* 80GB in mirror (gmirror) for all the installation setup complete
The 2* 500GB in mirror (zmirror) for the data only (/documents) with Snapshots, and other features activated.

The server already comes with 2*80GB hard drive on board so I plan to use for the base complete system.
The 2* 500GB are available in our stock as I don't wanna buy more hard disk, these 2 will be just nice.
We will need probably only 100GB as we store documents only.

My questions are simple (and maybe stupid but I have some doubt).

ZMIRROR still eat a lot of RAM from the system like ZRAID does ?
ZMIRROR still need tweaking like ZRAID need as system is i386 (no AMD) ?

Thanks for the answer and sorry for newbie questions.

Ciao
Dado


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## SirDice (May 7, 2010)

As far as I understood it it ZFS will run fine on amd64 with minimal 2GB. Below that requires quite some tweaking.


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## phoenix (May 7, 2010)

It's not the redundancy level (none, mirror, raidz1, raidz2, etc) that require memory.  It's the ARC, the memory cache that ZFS uses, that requires memory.

If you are using the 32-bit version of FreeBSD, you will need to tweak /boot/loader.conf to increase the size of kmem_map, limit the size of the ARC (vfs.zfs.arc_max), and so on.

If you use the 64-bit version of FreeBSD (if those Xeon CPUs support it), then you should be able to let the kernel auto-tune ZFS.  Depending on the workload, you may still want to limit vfs.zfs.arc_max.


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