ZFS Cache Drive Questions

[Yellowbeard]

ASUS P5Q-E
Intel P4 EE 3.73GHz CPU
4 x 2TB HDDs on Intel ICH10-R controller, RAID-Z
8GB of RAM

1. Would it be useful to add a cache drive for ZFS to use in my configuration?

2. I have tried to add a cache drive but gotten an error adding the drive. Can you add a single drive to my system as is with the 4 other drives already members of ZFS RAID-Z array?

The error is

CacheDrive /mnt/CacheDrive Error getting used space (Error) Error getting available space Error getting total space

 

[Yellowbeard]

Forgot to add, I have tried it with a HDD, an SSD, and also an old Gigabyte I-Ram 4GB.

 

[jpaetzel]

Cache drives will help read performance when the working set is smaller than the cache drive, but larger than the size of RAM available to the system. So if you had a situation where you accessed 20 GB of files all the time, and had a fast 60 GB drive, then yes, you'll see a performance improvement. This is assuming that you aren't hitting network bottlenecks, which with your hardware you may be doing.

As far as adding a cache device to an existing filesystem, what version of FreeNAS are you running? It's possible that it isn't working right in 8.0-R

 

[Yellowbeard]

Sorry, I thought I included that. Thanks for the reply.

FreeNAS-8.0-RELEASE-amd64
FreeBSD 8.2-RELEASE-p1

 

[Yellowbeard]

FWIW, I'm gigabit all the way thru. Onboard gigabit NIC on the MOBO and a gigabit switch for the network. I may invest in some Intel gigabit PCI-e NICs if my NICs prove to be the bottleneck.

 

[Yellowbeard]

Just tested the FreeBSD 8.2-RELEASE-p2, FreeNAS-8.0.1-BETA2-amd64 and no go. Same error. I also tried adding a single disk as a UFS volume and as a ZFS volume with "none" selected instead of cache. Same error every time.