View Full Version : Add stripe on existing RAIDZ volume
07-07-2011, 11:27 AM
Hi to all, I've setup my fist FreeNAS 8.0:
8GB RAM 1066Mhz
I created a RAIDZ 3x2TB volume (3,8TB usable space)
Now the archive is near full and my question is:
If I create another RAIDZ 3x2TB volume with the same volume name i suppose my RAIDZ becomes RAIDZ-0 right?
Does my media resident in the first RAIDZ volume automatically stripes data across new volume, so I'd have a new RAIDZ+0 volume with near double performance and capacity? Is it right?
07-07-2011, 06:11 PM
it's not quite stripped, it's not quite jboded. it's more like a hybrid.
if you have 3 nearly full disks and then attach 3 new ones, you'll still have 3 nearly full disks and 3 empty ones. but as you start to read and write data, zfs will choose the best place to write the new data. most should be written to the new disks but it is not a guarantee. if you're doing a lot of reads from your nearly empty disk, zfs may choose to write data to the nearly full one. over time they should be balanced out as long as your data changes. if your data on the full 3 is static, it will never move. so if your data is dynamic, it will eventually be spread across both vdevs and you'll have the double performance,
add the disks and zfs will handle the rest.
07-07-2011, 08:29 PM
Thank You for fast replay, so
If I hypothetical create a new 2 array 3x2TB before adding data to fist array does ZFS act as stripe for new data written between 2 arrays?
So maybe the answer for better performance could be a new 6x2TB raidz if I will decide to empty my fist array?
File transfer for single disk is near 90:100MB/s but in raidz with 3 disks only 40:50MB/s.Maybe a raidz with 6 disks will surpass single drive performance?
So another question for a fast archive: I think that there where nonsense to put 2 drives in stripping for theoretically 180:200MB/s when my GB lan limit is 125MB/s. I'll lost the majority of advantage, right?
07-08-2011, 11:57 AM
so I'm not quite sure what you're saying. i think you are saying if you make a new pool consisting of 2, 3 disk raidz vdevs and then write data to it, will it be spread out equally. if that's your question, more or less yes, it should wind up being spread out.
as for the speed, it depends on many factors. it looks like your CPU is sufficient so if you had 6 disks i would think you could easily fill a gigabit pipe. don't forget a gigabit NIC is full duplex, so you can read and write 1 gigabit/s so you want your pool to handle 2-3 times gigabit.
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