Alan,

We have been using Snapmirror in production on 2 F740's and 2 F760's. We may be using it for different purpose than you might - its principally used to provide a RAID 1-ish protection for our on-line volumes, and a modified, limited read-only access for some of that data. The first thing to know is that Snapmirror uses Snapshot technology, so the first thing the filers do at the scheduled intervals is build a snapshot. It will always build a snapshot even if no data has changed, and it always copies a percentage of the volume being mirrored. This makes every-minute snapmirrors almost impractical for large volumes (ours are 200-250 gig). Are filers are "paired" using a directly connected gigE cross-connect (no switch or router).

On a heavily loaded filer, snapmirrors can "timeout" as they try to build the snapshot - this is a known problem that netapp has a patch for that will be included in 5.3.4R1 (or so I'm told). We use a alternating, one hour window. That is, filer 1 in a pair runs at the 1 minute of the hour mark, while the other runs at the 30 minute of the hour mark. If you are snapping to a read-only filer, that has no other use (except for root), you get better results.

Have fun!

-----Original Message----- From: Mike Federwisch [mailto:mikef@netapp.com] Sent: Friday, November 12, 1999 3:44 PM To: Alan R. White Cc: toasters@mathworks.com Subject: Re: Considering filers for major deployment....

Is SnapMirror up to the job of keeping an almost real-time remote replica, i.e. snap every minute if the networks up to it? Are there any operational issues around this stuff?

This one I can answer. Keep in mind that SnapMirror is not targeted to be a "almost real-time" remote replica. Its performance depends greatly on network, load, filesystem size etc. I wouldn't expect it to be a real-time style replica. If the networks are up to it you can get 24M/sec over the wire. Snapshots are created for each transfer which also take time.

So figure out how much data changes per minute how fast your networks are and how much load you are planning on and you start to see how fast the updates can happen. I have seen situations where a per minute schedule can be achieved but I would lean more towards every 15 minutes or so but really it depends on your situation.

I think it is a great product (I am biased) but I want to make sure your expectations are set correctly.

Mike Federwisch Network Appliance