ZFS on backup fileserver - RAM usage

Matt Simerson matt at corp.spry.com
Mon Oct 13 20:43:13 UTC 2008

It all depends on your workload. If you work your backup serves hard  
(as I do, backing up thousands of OS instances), you'll have  
significant reliability problems using FreeBSD 7.1 and ZFS. After a  
crash that corrupted my file systems, I have moved to 8-head with  
Pawel's latest patch.

My backup servers have between 16 and 24 disks each. The ones with  
16GB of RAM crash far less frequently than my server that has only  
2GB. That one is getting upgraded soon.


On Oct 13, 2008, at 4:44 AM, Miroslav Lachman wrote:

> I am planning to install new server for backups with 4x 1TB SATA II  
> drives in RAIDZ. There will be about 20 separated filesystems from  
> one zpool, few jails with ssh (scp/sftp), rsync and maybe FTP  
> daemons, no other services with huge RAM utilization. As FreeBSD  
> 7.1(-BETA) amd64 still have some limits of kernel space memory, are  
> there any benefits to put more then 2GB or 3GB in this server? Will  
> it be more stabel or faster with for example 6GB of RAM? (I can buy  
> it, RAM is really cheap in these days, but will it have some sense  
> or is it vaste?)
> I am using this tuning on testing machine (with 2GB RAM):
> vm.kmem_size="1024M"
> vm.kmem_size_max="1024M"
> vfs.zfs.prefetch_disable="1"
> vfs.zfs.arc_min="16M"
> vfs.zfs.arc_max="64M"
> kern.maxvnodes="400000"
> (recommendations from http://wiki.freebsd.org/ZFSTuningGuide)
> Have somebody better results with another values?
> Miroslav Lachman
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