Slow saves to server with mirrored filesystems

[MarkSyder]

Hi everybody.

I persuaded the users to have their home accounts moved from their workstations to the server as it has mirrored discs: the selling point was that they can carry on working without losing anything if a disc crashes.

I've now transferred half the user accounts and the users are complaining that saving files takes a lot longer than it did previously. The users whose accounts are still on workstations are not having the same problem. Is this normal? Is it to do with mirroring or because they are saving over a network? What can I do to improve things? I really don't want to move the accounts back on to workstations.

Mark Syder (like the drink but spelt different)

[Pete Randall]

Mark,

Is this software mirroring (via MirrorDisk-UX)? If so, there is a (minimal) performance penalty - I wouldn't have thought that they would have noticed it. Is NFS involved, too?


Pete

[MarkSyder]

Pete,

Yes, it's MirrorDisk. And you're quite right, their accounts are NFS mounted.

Mark

[Pete Randall]

And were they NFS mounted before you moved them? I would suspect NFS more than the MirrorDisk.


Pete

[Steven E. Protter]

Shalom Mark,

A quick check with sar, sar -d will tell you if there is a disk i/o problem, which would be mirror/ux or NFS, which would show up on a different sar output.

You might just want to collect total data for an hour.

http://www.hpux.ws/system.perf.sh

I already agree with Pete's conclusion to suspect NFS first.

SEP

[Pete Randall · Accepted solution]

Mark,

Assuming it is NFS to blame, here's a jumpstart on troubleshooting:

http://docs.hp.com/en/5991-1153/ch08s04.html?jumpid=reg_R1002_USEN


Pete (like the moss, but spelled differently)

[Bill Hassell]

Local disks can write data at 10 to 40 Mbytes/sec, but NFS is restricted to a very small pipe. At full speed, a LAN can transfer bytes at about 1/20th of the bit rate. So for a 10Mbit LAN, expect 0.5Mbytes/sec, and for 100Mbit LANs, expect no more than 5Mbyes/sec. Then NFS adds additional overhead to work as a stateless protocol to handle the details about open/close and read/write/position. For small files, the slowdown isn't noticeable but for large files, expect 3 to 10 times slower performance depending on your LAN speed. Note that mirroring has no measureable overhead when used for NFS -- the LAN is the biggest bottleneck.

Now you could switch all of your workstations, switches and server to Gigabit and performance will be very close to local disk speeds. Note also that your server must be extremely reliable (no downtime during workstation hours). If your server (or LAN card or network, etc) fail, all of the workstations will be paralyzed.

[MarkSyder]

Some useful advice to be researching there.

Interesting advice about upgrading network cards to 1Gb. I've googled 1Gb network cards and they seem to be remarkably cheap - I think I could persuade the appropriate people to release funds - but they all specify Windoze. Is this simply because the supplier doesn't know that other operating systems exist? Or do I need a specific type of card for an HP-UX system?

Mark

[RAC_1]

In addition to What Bill said, also look at how you are mounting these NFS mounts. mount -v will show you the options with which nfs mounts are mounted. Also are these nfs mounts mounted using automount??

Check nfsstat.
Also what protocol do you use for nfs mounts? How exactly mirroring is done?

[Steven E. Protter]

Shalom again Mark,

It would appear a significant performance boost can be had by connecting to an NFS v4 server. This does of course still depend on the size of the pipe.

Linux is using NFS 4 at least most distributions. EMC storage is using it in its latest release which my storage guru's told me is too new to use.

You might also look for a traceroute to see if there is a networking glitch or configuraion problem on one of your routers making the situation worse.

SEP

[MarkSyder]

Thanks for all the replies. The document Pete referred me to gave me the answer: add async to the entries in /etc/exports. I did this and asked a user to copy a directory. This directory took 22 minutes to copy yesterday - today it took 3 minutes.

Mark

[Bill Hassell]

As a general answer about 1Gb LAN cards, the issue is not with the OS, it is with the architecture and marketplace. Except for Linux, most commercial Unix system have proprietary hardware and even when there are similar I/O structures (EISA, PCI), drivers must be written to accomodate the card in the OS. In general, if the card isn't supported (read: driver exists) by the OS manufacturer, there is very little chance that the card mfr will provide a driver.