Selim Daoud wrote:
indeed, a customer is doing 2TB of daily backups on a zfs filesystem
the throughput doesn't go above 400MB/s, knowing that at raw speed,
the throughput goes up to 800MB/s, the gap is quite wide
OK, I'll bite.
What is the workload and what is the hardware (zpool) config?
A 400MB/s bandwidth is consistent with a single-threaded write workload.
The disks used in thumper (Hitachi E7K500) have a media bandwidth of
31-64.8 MBytes/s. To get 800 MBytes/s you would need a zpool setup with
a minimum number of effective data disks of:
N = 800 / 31
N = 26
You would have no chance of doing this in a disk-to-disk backup internal
to a thumper, so you'd have to source data from the network. 800 MBytes/s
is possible on the network using the new Neptune 10GbE cards.
You've only got 48 disks to work with, so mirroring may not be feasible
for such a sustained high rate.
also, sequential IO is a very common in real life..unfortunately zfs
is not performing well still
ZFS only does sequential writes. Why do you believe that the bottleneck
is in the memory system? Are you seeing a high scan rate during the
workload?
-- richard
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