The AWS US-West move (from US-East) is almost done.. we’ve moved 5 server instances but the main mail server is proving to be a real drag and moving 250GB of customer emails translates to 2Tb (uncompressed) of data that needs to go through the wire.. unfortunately, at this point, AWS does not provide an easy way to copy volumes or snapshots from one region to another so we have to write our own email transfer app… no, rsync wont cut it. This is the second time we’ve transferred emails from one data center to the other and the strategy that worked for us is first to write an email transfer app that not only compresses but can also crawl a unix user’s mail dir.. at any rate, its there and the transfer sequence we employed is:
- Copy Oldest Emails First. This is the bulk of the transfer, so we have to copy the emails from say 15 days past to the earliest (e.g. if we are to do this today — April 29 — then all emails before 2010-04-14 23:59:59). Copying all these emails will take days…
- Copy Recent Emails starting from (1) — ie 2010-04-15 00:00:00 – up to yesterday. This is a smaller set and now we’re almost at sync with the new server. This typically takes less time (in our case only for a few hours). Once that’s done..
- Direct all SMTP/IMAP/POP3 connections to the new Mail Server – at this point the users may miss yesterday’s emails. But this step is necessary so no new emails goes in the old mail server.
- Copy yesterdays emails to the new mail server — once done all emails would have been recorded and users see their previous day’s emails.
There’s going to be a couple of calls about ‘reappearing emails’ but customer support should be able to handle it.
One effect of the transfer from AWS East to AWS West is of course improvement in latency.. from an average of 300++msec to 230msec.. its a 25% improvement. Of course this is relative to where most of our customers are (in Asia). AWS West (having been in operations for less than a year) also has newer machines so we’re also seeing improvements in application performance. Overall, we’re satisfied.