Questions[redundancy](server)

So our DNS provider, every so often, experiences DDOS attacks on their systems that causes our front-facing web sites to go down.

What are some options in terms of reducing dependency on a SINGLE external managed DNS provider? My first thought was using lower expire TTL and other SOA TTLs, but it feels like these affect secondary DNS server behavior more than anything else.

i.e. If you experience a DNS outage (due to DDOS, in this example) that lasts more than, say, 1 hour, delegate everything to a secondary provider.

What do people do out there when it comes to their external DNS and using another managed DNS provider as backup?

Note to our friendly moderators: this question is much more specific then the " "generic mitigate DDOS attack" questions out there.

EDIT: 2016-05-18 (A few days later): So, first off thank you AndrewB for your excellent answer. I have some more information to add here:

So we reached out to another DNS service provider and had a chat with them. After thinking and doing a bit more research, it's actually a LOT more complicated than I thought to go with two DNS providers. This is not a new answer, it's actually more meat/info to the question! Here is my understanding:

-- A lot of these DNS providers offer proprietary features like 'intelligent DNS', for example DNS load balancing with keepalives, logic chains to configure how responses are handed back (based on geo location, various weights to records, etc. etc.). So the first challenge is to keep the two managed providers in sync. And the two managed providers are going to have to be kept in sync by the customer who has to automate interacting with their APIs. Not rocket science, but an ongoing operational cost that can be painful (given changes on both sides in terms of features and APIs).

-- But here is an addition to my question. Let's say someone did do use two managed providers as per AndrewB's response. Am I correct in that there is no 'primary' and 'secondary' DNS here as per spec? I.e., you register your four DNS server IPs with your domain registrar, two of them are one of your DNS providers, two of them are DNS servers of the other. So you would essentially just be showing the world your four NS records, all of which are 'primary'. So, is the answer to my question, "No"?

I've done some looking and have not found a satisfactory answer to this question.

When is it necessary or suggested to use an independent UPS (on it's own mains branch circuit) for each power feed to a rack? To elaborate; when using servers with redundant power supplies, it's typically recommended that each '1' power supply goes to branch circuit 'A', and each '2' power supply is fed by branch circuit 'B', but do you need a UPS for both 'A' and 'B' feeds, or just one?

Background: I've been tasked with planning an infrastructure upgrade to our internal-use servers. We are a manufacturing company and much of our equipment and custom software relies on having reliable and online servers locally in our office. We currently have two server rooms with one rack in each, that are on opposite ends of a large building (for redundancy against fire or accident etc). They each have a UPS that is fed from circuit 'A' and the equipment we have that does have multiple PSUs has both connected to this UPS. So if the UPS were to die... ploop, there goes the servers.

My personal theory is that having PSU1 of each server connected to a UPS, and PSU2 of each server connected to a PDU that is fed directly from mains, would provide a good mix of reliability and cost. But my supervisor thinks that we should run two UPS units, one for each feed.

If this question is too vague please let me know and I will try to revise it.

I'm debating about using LVM for a media/file server because I would like to combine multiple physical hard disks into one volume. I do not wish to use any RAID in my LVM so my question is:

If one of the multiple hard disks in my volume were to go down would I lose all my data or would I just lose the data that was stored on that individual disk?

Also, if I were to just lose the data on the individual disk, would it be as simple as replacing that disk and restoring what was on it from a backup to recover?

We have a set of shared, static content that we serve up between our websites at http://sstatic.net. Unfortunately, this content is not currently load balanced at all -- it's served from a single server. If that server has problems, all the sites that rely on it are effectively down because the shared resources are essential shared javascript libraries and images.

We are looking at ways to load balance the static content on this server, to avoid the single server dependency.

I realize that round-robin DNS is, at best, a low end (some might even say ghetto) solution, but I can't help wondering -- is round robin DNS a "good enough" solution for basic load balancing of static content?

There is some discussion of this in the [dns] [load-balancing] tags, and I've read through some great posts on the topic.

I am aware of the common downsides of DNS load balancing through multiple round-robin A records:

• there's typically no heartbeats or failure detection with DNS records, so if a given server in the rotation goes down, its A record must manually be removed from the DNS entries
• the time to live (TTL) must necessarily be set quite low for this to work at all, since DNS entries are cached aggressively throughout the internet
• the client computers are responsible for seeing that there are multiple A records and picking the correct one

But, is round robin DNS good enough as a starter, better than nothing, "while we research and implement better alternatives" form of load balancing for our static content? Or is DNS round robin pretty much worthless under any circumstances?

In our shop we're faithfully using RAID in all our workstations, probably just because that seems to be the way it ought to be done. I'm talking about workstations for scientific simulations, using the onboard RAID chips.

But I've heard a lot of RAID horror stories. Stackoverflow itself has had an outage caused indirectly by RAID controller.

RAID protects you against a very narrow type of failure - physical disk failure - but at the same time it also introduces extra points of failure. There can be problems with the RAID controller, and there often are. In our shop at least, it seems that RAID controllers fail at least as often as disks themselves. You can also easily mess something up with the process of swapping a faulty drive.

When is RAID worth the trouble? Don't you get a better return on investment by adding more redundancy to your backup solutions? Which type of RAID is better or worse in this regard?

Edit: I've changed the title from the original "Is RAID worth the trouble?", so it sounds less negative