Aditya;
**** Does anyone have ballpark numbers (for any filer model) how long a drive would take to reconstruct on a filer on the default raid reconstruct_speed setting? ie. on an F85:
options raid.reconstruct_speed 4
I'm trying a ballpark compare against a Sun 3310 array with 73Gig drives, where it took almost excatly 5 hours.
I realize it depends on filer load, but if the speed is linear with load and drive size then it is easy to extrapolate.
I couldn't find a table or any other sort of indication on NOW about this... **** I'm trying to benchmark the same thing (Restore time) on an R200 to figure out how to weight things like double-parity against restore time.
I've found 6 hours for the approx. 250GB drives on an R200, dual-spindle volume. That's about worst case I can come up with, and that's with no external reads from the volume at all. 72GB drives are going to be much faster, and I'll bet, linear in time with disk size, for a given disk rotational speed. Remember, too, that the R200's drives are 320GB parallel ATA drives: NOT the blazing-fast U160 SCSI drives in the 3310.
I haven't concocted a "read while constructing" test: it's extremely difficult and time consuming. But I will tell you that I do believe that the speed of rebuild is NOT linear with load and drive size. For you to make any headway, you need to use identical drives in both the 3310 and the filer, and you need to use the same number of spindles per volume (filer) or LUN (3310), same RAID technology too.
What you're going to find is that no-read rebuild speeds on the NetApp will be faster, because WAFL kicks butt and the parity recalculations happen in the filer head's RAM at RAM speeds. It's the disk technology that will be the brick wall in any disk storage device. Disk operations take milliseconds, while RAM operations take nanoseconds.
But with any level of reads at all against either device, the 3310 is going to be a tad faster. But...at best...you can connect a 3310 to two devices without a SAN switch. The NetApp can talk to anything on your network that sees CIFS or NFS.
I can tell you that I've lost drives during my backup window, and seen the backups get delayed by 30-50%. That is, backups taking upwards of twice as long. My raid "reconstruct speed" is set to the default, "4". I'm sorry, I can't tell you if it took longer or not to rebuild the volume.
One other thing: that Sun 3310 is a SAN-technology unit that connects to the host via FC. To get a fair comparison between a NetApp and a 3310 is going to require you to gather metrics with no host reads from the rebuilding volume, (or LUN in the case of the 3310) because the NetApp is going to be strongly bound by the speed of your connecting network. It'll be an extremely unfair test if your NetApp client is reading over a 100mb connection vs. the Sun 1- or 2-gbyte FCAL connection. (The technology is different enough that you could appear to be trolling for ammo for the old "SAN vs. NAS" war with your question.)
JKB