ZFS raid write performance?

[Bob Friesenhahn]

On Mon, 22 Jun 2015, Quartz wrote:

> What's sequential write performance like these days for ZFS raidzX? Someone 
> suggested to me that I set up a single not-raid disk to act as a fast 
> 'landing pad' for receiving files, then move them to the pool later in the 
> background. Is that actually necessary? (Assume generic sata drives, 
> 250mb-4gb sized files, and transfers are across a LAN using single unbonded 
> GigE).

The primary determinant of write performance is if the writes are 
synchronous or not, With synchronous writes, the data is comitted to 
non-volatile storage before responding to the requestor.  With 
asyncronous writes, the data only needs to be written into RAM before 
responding to the requestor.

Writes over NFS 3 are synchronous.  Writes over CIFS/Samba are likely 
not.  For good performance with synchronous writes, some sort of 
non-volatile write cache (e.g. dedicated zfs intent log "slog", 
controller NVRAM) is advised.

Use multiple sets of mirrors for maximum write performance with 
multiple clients.

Even 10 years old hardware should be able to keep up with gigabit 
Ethernet rates (< 100MB/s) given a reasonable disk subsystem.

Bob
-- 
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/