Redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe.

learn more… | top users | synonyms

43
votes
7answers
6k views

Probability of Blade Chassis Failure

In my organisation we are thinking about buying blade servers - instead of rack servers. Of course technology vendors also make them sound very nice. A concern, that I read very often in different ...
36
votes
16answers
35k views

Is Round-Robin DNS “good enough” for load balancing static content?

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 ...
21
votes
5answers
2k views

How to protect against loss of server on a budget

I'm a small company on not much budget providing websites and databases for charity and not-for-profit clients. I have a few Debian Linux VPS servers and ensure I have daily backups to a different ...
13
votes
21answers
5k views

When is RAID worth the trouble?

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 ...
12
votes
4answers
804 views

Is there any value in protecting both rack power feeds with their own UPS?

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 ...
11
votes
8answers
3k views

Load balancing Apache on a budget?

I am trying to get my head around the concept of load balancing to ensure availability and redundancy to keep users happy when things go wrong, rather than load balancing for the sake of offering ...
10
votes
9answers
14k views

Correct way to set up DNS primary/secondary/… for redundancy and latency reduction?

I thought DNS primary/secondary for redundancy purposes was straightforward. My understanding is that you should have a primary and at least one secondary, and that you should set up your secondary in ...
10
votes
1answer
4k views

Alternatives to Dell's mirrored SD card module for booting a small OS from flash?

Dell offers an add-on hardware card for some of their servers that provides a poor man's RAID1 between two SD cards (one card gets all the reads until it dies, writes are mirrored) for booting a ...
9
votes
7answers
7k views

Do you lose everything when you have a hard disk failure in a multi-hard disk LVM that does NOT use RAID?

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 ...
9
votes
3answers
299 views

How to make redundant load balancers?

I understand that the purpose of load balancers is to balance load between your servers and keep track of instance health, etc. But what if load balancer itself fails? How do you set up redundant load ...
8
votes
5answers
894 views

Hot spare host vs cold spare host?

We have several hosts where we have an identical hot spare host, which is patched and updated so it is very close to have to same software and config. In case of failure the network cable is switched ...
8
votes
1answer
1k views

VMware vSphere cluster design for site redundancy

I have a question about the best design for site redudancy when using vSphere clusters. A bit of background info about our situation first though. We are a medium-sized company with two main ...
7
votes
2answers
3k views

One server, Two APC UPS on redundant power supplies : How to trigger shutdown?

I have a server racked and its redundant power supplies plugged in two APC Smart-UPS 3000 XLM. Each UPS is connected to two different mains power sources. Two instances of apcupsd are running, each ...
7
votes
5answers
2k views

Local to Remote Webserver Failover

Short and sweet, I don't suppose you'll need more detail than this: We host our website on an in-house webserver. A catastrophe has and will happen again where communication from the web into/out ...
6
votes
1answer
477 views

How do I configure NAT rules when using ASA IP-SLA when leveraging post-ASA-8.3 NAT syntax?

We are currently running ASA9 at a location with redundant ip connectivity. We'd love to configure ip sla so that internet access survives a single carrier outage. I'm aware of the ip sla commands, ...
6
votes
5answers
7k views

Can you set a backup ip for your server in DNS?

Is there a way that the DNS protocol can natural hold a backup A type server address, like a backup name-server or mail server ? After googling i just got results on backup nameservers. If there isnt ...
6
votes
3answers
2k views

Getting Started with NIC and Switch Redundancy

Currently with my servers, they all or almost all have 2 nics with one in use. Each NIC is is of course connected to a single switch. What do I need to do to make this redundant in that both NICs ...
5
votes
3answers
3k views

Is round-robin DNS a possible solution for high availability?

Let's say I have 2 IPs for a given domain (round-robin DNS). If one the IPs becomes unresponsive, will clients try to connect to the other IP? or they will just fail to establish comunication with the ...
5
votes
1answer
278 views

Plug single PSU into two different power sources

We have a rather uncommon situation: We have a server in a computer center. Its got not enough spare space to put in a redundant PSU. Nevertheless, we want to attach the single PSU to both existing ...
5
votes
1answer
205 views

DRBD for HA Server in Small Office Questions

Backround: We are in need of a HA server in a small office environment and are looking at DRBD to provide it. We only have about 100GB that needs to be on the HA server and server load will be ...
5
votes
4answers
2k views

Providing high availability and failover using MySQL on EC2

I would like to have a highly-available MySQL system, with automatic failover, running on Amazon EC2 instances. The standard approach to solving this is problem Heartbeat + DRBD, but I've found a lot ...
5
votes
3answers
4k views

Redundant links from Router to Switches

With a setup of two NICs on a server into two different switches where each NIC has a different IP (But both on the same network), and then the switches to the router. How would I configure the two ...
5
votes
3answers
541 views

SQL Server clustering options

Can anyone give an high-level overview of the options available for SQL Server clustering, their pros and cons? Is it better to use Microsoft Clustering services or SQL Server native clustering? Does ...
4
votes
4answers
172 views

Achieving Five Nines

I am building a web application where uptime is key. I understand that 100% uptime is not realistic but I would like to achieve five nines. I'm unsure as to the most prudent way to accomplish this. ...
4
votes
3answers
3k views

Linux console is unusable when LDAP server is down

When our OpenLDAP server lost power the CentOS machines' console became nearly unusable. We were trying to login with a local account, but each command would take minutes to return. Even simple ...
4
votes
11answers
2k views

How far should we take the N+N redundancy craziness?

The industry standard when it comes from redundancy is quite high, to say the least. To illustrate my point, here is my current setup (I'm running a financial service). Each server has a RAID array ...
4
votes
3answers
211 views

Should redundant servers have exactly the same configuration, or slightly different?

If you provide a service on two servers to ensure high-availability, is it better to configure them in exactly the same way, of instead should you introduce slight differences to prevent "freak ...
4
votes
2answers
3k views

Redundant NFS on Amazon EC2

I'm interested in building two fault tolerant/redundant NFS servers with failover at Amazon EC2. I'm familiar with tools/technologies like DRBD, Heartbeat, etc. Does Amazon provide any specific way of ...
4
votes
3answers
226 views

What hardware & software consideration does a major website require to properly manage 1000+ servers? [closed]

Sorry for such a high level question. I understand the basics of server load balancing, but the concept of managing 30,000 servers is a bit foreign to me. Is it really just the same concept of ...
4
votes
6answers
3k views

Redundant Load Balancers for Windows-based Web Servers?

I'm having some trouble trying to figure out the technical details of the below design; specifically in the area of the redundant load-balancers. The web servers are running Windows Server 2003 R2 64 ...
4
votes
2answers
719 views

Howto create redundant network on server

I am in the situation where I have a number of CentOS Linux servers which all have two NIC interfaces. Currently one of these interfaces is used for internal communication, the other is used for ...
4
votes
1answer
2k views

Is Microsoft's “Storage Spaces” just LVM for Windows? [closed]

From initial reading, it looks like Microsoft's forthcoming "Storage Spaces" is an LVM-like tool for Windows. Is this a correct assessment? If it's not merely LVM-for-Windows, then what is it, and ...
4
votes
4answers
368 views

System Monitoring Redundancy

I consult in a small business environment where I have two HyperV hosts (with <10 VMs) + a couple other servers. I recently had an issue where one of the HyperV hosts had a CPU issue and it came ...
4
votes
3answers
767 views

Sharepoint - one way sync to a second SP server for standby/backup

Using MOSS 2007 on SQL server 2005 is there any way to do a "one-way" synch of data from a production server to a standby server? This would be a one-way process only, and can happen daily rather ...
4
votes
3answers
1k views

Recommendation for a small redundant VM infrastructure?

We currently have an active-active 2 node cluster running virtual machines. Every node has two disks, every disk is DRBD mirrored on the other node. Every node runs virtual machines out of his primary ...
4
votes
2answers
433 views

Two domain controllers - yet when primary is down, domain still fails?

I have multiple windows 2003 servers support a particular network, and when one particular server is taken offline, domain services begin to rapidly fail, such as users couldn't login. What check ...
4
votes
2answers
1k views

Network Redundancy Example

Looking for help filling in how redundancy in the following model might work: I believe my Datacenter will give me redundant gateways with two hand offs (going to have to talk to the more about ...
4
votes
2answers
3k views

How to achieve redundancy across data centers?

I have a LAMP server with a lot of hardware redundancy built in. I am not worried about the server becoming unavailable. What I am worried about, however, are potential network issues in the data ...
3
votes
8answers
965 views

Which is more standard in large enterprises: RAID5 or RAID10?

Which is more standard in large enterprises: RAID5 or RAID10?
3
votes
4answers
12k views

Split your DHCP scope among multiple servers?

I want to implement a redundancy solution. I have two subnets all windows XP machines - each with their own DHCP server - joined by a bridge. Currently - all machines get DHCP leases from the one ...
3
votes
3answers
3k views

A-Record Failover?

I have a Fortigate 100D with 2x BT Business Infinity Fibre connections acting as WAN1 & WAN2. The BT lines come with 5 static public IPs each and I have my DNS hosted through CloudFlare pointing ...
3
votes
3answers
339 views

How much failover redundancy is enough? [closed]

I'm working on a client-server system where all clients currently submit their transactions to essentially a single west-coast IP address to reach what is called the "gateway" application. The ...
3
votes
2answers
723 views

PowerConnect switches, Juniper firewalls and esx redundancy

Let me preface this question by saying that I am a developer and have basic knowledge of networking. My current job requires that I wear many hats. I am building out a DataCenter for our SaaS ...
3
votes
3answers
655 views

Redundant Linux Servers in Seperate Datacenters

I have 2 CentOS linux servers in separate data centers on each site of the country. These linux machines run a small web sites on Apache with a MySQL backend. There currently is no VPN connectivity ...
3
votes
2answers
469 views

How much power draws a redundant PSU?

One supermicro enclosure comes with "3 SP382-TS 380W Power Modules for a total of 760W". 2x380W = 760W, okay, but there are 3! So where is the missing third 380W equalling to 1140W?? Is it ...
3
votes
8answers
772 views

Redundant network connections for website

We are in the process of building a new secure web application for our company, and are looking at options for ensuring redundancy in our data center. We don't have a lot of money, but have ...
3
votes
3answers
404 views

Probability of Blade Chassis Failure, Redundancy

Suppose I have a blade server HP C7000, with three blades. Q1. Is there any disaster recovery technique that provides redundancy between blades? If any one blade goes down the second should come up ...
3
votes
4answers
423 views

MySQL Redundancy for High-Availability over the internet

I am testing out some infrastructure options before I start writing a web application. I would like to have two separate MySQL database servers at different physical locations, but if one of them ...
3
votes
4answers
332 views

is it possible to use a windows server as a datastore for vmware esx server

I'm a relative noob at virtualisation but would like to roll it out in our organisation. The application I'd like to test with needs to be back up pretty quickly after failure... So I'd like to put 2 ...
3
votes
1answer
1k views

Configure fallback redis server

I am using redis as a cache server. Can I somehow configure multiple redis servers, that the cache is fully functional (read/write) even if some of them go offline? I looked into master->slave, but ...