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Re: [zfs-discuss] Filesystem for each home dir - 10,000 users?

Subject: Re: [zfs-discuss] Filesystem for each home dir - 10,000 users?
From: Richard Elling
Date: Thu, 05 Jun 2008 08:11:55 -0700
Richard L. Hamilton wrote:
>> Hi All,
>> I'm new to ZFS but I'm intrigued by the possibilities
>> it presents.
>> I'm told one of the greatest benefits is that,
>> instead of setting 
>> quotas, each user can have their own 'filesystem'
>> under a single pool.
>> This is obviously great if you've got 10 users but
>> what if you have 
>> 10,000?  Are the overheads too great and do they
>> outweigh the potential 
>> benefits?
>> I've got a test system running with 5,000 dummy users
>> which seems to 
>> perform fine, even if my 'df' output is a little
>> sluggish :-) .
>> Any advice or experiences would be greatly
>> appreciated.
> I think sharemgr was created to speed up the case of sharing out very
> high numbers of filesystems on NFS servers, which otherwise took
> quite a long time.
> That's not to say that there might not be other problems with scaling to
> thousands of filesystems.  But you're certainly not the first one to test it.
> For cases where a single filesystem must contain files owned by
> multiple users (/var/mail being one example), old fashioned
> UFS quotas still solve the problem where the alternative approach
> with ZFS doesn't.

A single /var/mail doesn't work well for 10,000 users either.  When you
start getting into that scale of service provisioning, you might look at
how the big boys do it... Apple, Verizon, Google, Amazon, etc.  You
should also look at e-mail systems designed to scale to large numbers of 
which implement limits without resorting to file system quotas.  Such
e-mail systems actually tell users that their mailbox is too full rather 
just failing to deliver mail.  So please, when we start having this 
again, lets leave /var/mail out.
 -- richard

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