I am having a performance problem with network writes to my XSan. I have
done a lot of testing and here is what it boils down to. Reads and writes
between my XServe G5 and the XServe RAID over fiber channel perform as
expected. If I share a folder on an internal hard drive in the XServe G5,
all my network clients can read and write fast over SMB and FTP. If I share
a folder on a client and connect to it from the XServe G5, it can read and
write fast to that share. When I share a folder on the XSan from the XServe
G5 however, reads function normally, but clients that attempt to write to
the share are bottlenecked at roughly 4MB/s per client. Multiple clients
each add 4MB/s write, so two clients I see a total of 8MB/s network traffic,
5 clients I see 20MB/s etc.
So I know from this testing that my ethernet topology is fine since all
clients and servers can talk to each other at expected performance for
Gigabit ethernet, and that my fiber channel topology is fine because if I
copy files from the local hard drive in the XServe G5 onto the XSan, writes
run as fast as the internal drive can serve them up. That leaves something
occurring at the point where the server takes inbound ethernet network
traffic and sends it to the XSan for writing to the disk.
I have an extremely simple configuration for users and permissions. There
is only one folder on the XSan volume, and there are only two user accounts
that have access. One has read only access, the other is read and write
access.
The only anomaly I can find is if I watch the FC traffic graph during these
writes. whether it is one client poking along at 4MB/s or 5, the FC always
shows 120MB/s traffic, which coincidentally is the same as the peak
sustained write rate to my SAN using the XSan tuner tool.
Has anyone run into anything like this before? I am really stumped.
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