1) 1 Linode 512 hosting 4 wordpress blogs plus 4 sql dbs & 1 512 email server with sql built in.

VS

2) 1 linode 512 hosting 4 wordpress blogs, 1 linode 512 for email server AND 1 512 linode sql server having all wordpress and email dbs.

I am typing this from a mobile device so excuse any formatting.

Thanks for any help.

Just get a single 1024 or 1536 Linode.

Spreading tiny VPS's across several machines for such a tiny load isn't worth the admin hassle.

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Either provide enough details for people to help, or sit back and listen to the crickets chirp.
Security thru obscurity is a myth - and really really annoying.

Nice point.

But wouldn't it be nice to keep sql on a separate linode for both mail and wordpress ? Will performance improve or degrade ?

If the load is low, it wouldn't make any difference.

Why? The DB Engine will still be RAM bound by the limit of the VPS.

All you've done is double your admin tasks. Double your single point of failures. Made all DB transactions flow thru the internal LAN (so now besides being RAM bound, they're also network bound).

You've added all types of complexity for zero payback.

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Either provide enough details for people to help, or sit back and listen to the crickets chirp.
Security thru obscurity is a myth - and really really annoying.

Makes a lot of sense. Thanks for the guidance