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I have a server that has 7 large disks that are each shared out via NFS to our webserver.

My question is: Would it be more efficient if I shared the parent directory so that there was only a single NFS mount point on the webserver, or would it make any difference? (ie. I have 7 entries in my /etc/exports file now - and am thinking about replacing them with a single one)

Is there any measure of redundancy in having 7 separate shares? Would it affect the network speed? CPU load? Memory usage?

Thanks.

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2 Answers 2

There's no redundancy to be had from NFS itself. As for network speed, AFAICT (as far as I can tell) there's no speed increase...unless the NFS server isn't available at mount-time. If it's unavailable, you'll have to wait for 7 NFS timeouts to pass...in other words, pack a lunch. CPU speed won't be a big issue, nor will memory usage. Make sure that you exclude the NFS mounts from the updatedb.conf so you aren't indexing them across the connection.

If all servers are going to have to mount all shares, there's no reason (that I can think of) to make them individual. As soon as you have one server that shouldn't have all of them mounted, they should really be separate. It's dependent on your situation.

One question I do have. You said that you have 7 large disks. Do you mean that you have 7 individual disks, or do you have 7 slices on a RAID volume? Because if you want redundancy, that should be your first step.

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Yes, there are 7 virtual hard drives on a SAN - so they are already raided. –  Brent Dec 19 '09 at 20:39
    
OK, that's great. I just wanted to make sure :-D –  Matt Simmons Dec 20 '09 at 1:07

Some NFS server implementations differentiate between physical filesystems, and might not like exporting a directory containing the mountpoints of 7 distinct filesystems. However, I think this is a non-issue with the default options in the modern linux implementation.

It might be very slightly better to have a single share so that your clients see it all as a single mount point, however the difference will be so negligible that it doesn't matter. Do whatever is cleanest from a management perspective. For example, depending on how many clients you have, you probably don't want to visit all of them to add another mount when you add an 8th drive to your server. If you export the parent as a single share, then they would all see it automatically.

You should consider combining the 7 drives at the block level in a RAID-0, RAID-5, or RAID-Z configuration in order to get more speed (and some resiliency, depending on which RAID-*). You would then have a single large filesystem to export from your server.

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