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48

There's a low probability of complete chassis failure... You'll likely encounter issues in your facility before sustaining a full failure of a blade enclosure. My experience is primarily with HP C7000 and HP C3000 blade enclosures. I've also managed Dell and Supermicro blade solutions. Vendor matters a bit. But in summary, the HP gear has been stellar, ...


36

Jeff, I disagree, load balancing does not imply redundancy, it's quite the opposite in fact. The more servers you have, the more likely you'll have a failure at a given instant. That's why redundancy IS mandatory when doing load balancing, but unfortunately there are a lot of solutions which only provide load balancing without performing any health check, ...


20

As load-balancing, it's ghetto but more-or-less effective. If you had one server that was falling over from the load, and wanted to spread it to multiple servers, that might be a good reason to do this, at least temporarily. There are a number of valid criticisms of round-robin DNS as load "balancing," and I wouldn't recommend doing it for that other than ...


19

I've been managing small numbers of blade servers for eight years now, and I've yet to have a system-wide failure that took a number of blades offline. I've come real close due to power-related problems, but haven't yet had a chassis-wide failure that wasn't attributable to outside sources. Your observation that the chassis does represent a ...


16

Don't worry, RAID isn't used throughout the business world because of groupthink! The chance of decent RAID controllers failing is far, far lower than the chance of a disk failure. I don't recall ever seeing a RAID controller fail in real life, while I've seen many a disk die, both in the office and datacenter. PS: I see your tags. RAID is not backup! :)


15

They both are. It depends on the application using the array, the number of disks in the raid group and the IO requirements of the applications sitting on them. For example a file server probably doesn't need RAID 10 as the bulk of the data is just sitting there with a few users opening and closing files through out the day. An OLTP database may need a ...


15

You can connect a server with redundant power supplies such that each power supply is connected to a different power source (different UPS). If any power supply or UPS goes down, the other one will be available (hopefully).


14

That question could be extended to shared storage. Again I would say, that we need two storage units instead of only one - and again the vendors say, that this things are so rock solid, that no failure is expected. Actually no. You concerns so far made sense, this sentence puts them into "read the stuff in front of your eyes". HA with full ...


14

The way that we deal with this is to create an separate object group for interface that we want to have redundant connectivity to, it is a little messy but it should work for what you need. So you would have a FIOS object object network FIOS_NYHQ_GUESTWIRELESS_10.110.6.0_24 nat (NYHQ-GUESTWIRELESS,NYHQ-OUTSIDE_FIOS) dynamic interface and a Cogent ...


11

The most common way to do this is to split your IP range between the 2 DHCP servers and have both running at the same time. Clients will then recieve an address lease from whichever server responds first. In the event of the bridge failing, those with leases from the server on their own subnet will be fine, any with leases from the other subnet will get a ...


11

Yes, it's a bit old school. Modern hardware doesn't just fail that often. Focus either on making your applications more highly-available (not always possible), or on the items needed to make your individual hosts more resilient... For hosts: Buy better hardware. Ensure you have support contracts. REGISTER your servers' support contracts (spare parts are ...


10

I've said it several times before, and I'll say it again - if resiliency is the problem then DNS tricks are not the answer. The best HA systems will allow your clients to keep using the exact same IP address for every request. This is the only way to ensure that clients don't even notice the failure. So the fundamental rule is that true resilience ...


10

Real 100%? No. Five nines (99.999%)? Yep. Five nines is about five minutes unscheduled outage/year. You can get more reliability if you want, but five nines is where the cost for increased reliability is really taking off. You can approximate four nines as less than an hour outage/year, three nines as less than nine hours and six nines as about half a ...


10

Currently when one of the two UPS dies, the doshutdown event is triggered, and executes the default script via apccontrol. The doshutdown script ignores the second UPS, as they are not event-connected, and proceed normally with the shutdown. In order to have the doshutdown events somewhat connected, the two instances of apcupsd need a specifically ...


10

Yes... sort of. There are two things you can do here: If you put multiple A records in your DNS server for a given name, then they'll all be served to clients and those clients will pick one from the set to connect to, meaning that traffic will be "fairly" evenly distributed amongst all sites simultaneously. This isn't really what you seem to be ...


10

Keep them the same. The chance that you will have some incompatibility that manifests itself only in a certain configuration are minimal and afterwards you will have to remember the differences for everything you do.


9

Round robin DNS is not what people think it is. As an author of DNS server software (namely, BIND) we get users who wonder why their round robin stops working as planned. They don't understand that even with a TTL of 0 seconds there will be some amount of caching out there, since some caches put a minimum time (often 30-300 seconds) no matter what. Also, ...


9

This is typically done using some form of VRRP maintaining a virtual IP address across 1 or more servers, each running HAproxy. This is typically done with keepalived, there's a guide here which should help. Note that several people use Heartbeat for this, but Willy Tarreau (the guy behind HAproxy) has mentioned it isn't the best tool for the job. You can ...


9

It's rather inefficient - not least because of the dependency on manual intervention to make the switch. I have worked at places that run a hot DR site - literally, identical servers to the primary, ready to go instantly. However the DR switchover is an automated process - we're not talking cabling, a bit of fiddling and a switch, but a process when we ...


9

Answers to this may vary. But I actually work in warehousing and logistics environments, and I'll typically plan new server rooms to have a high capacity central UPS (6kVA or more), usually an online (double-conversion) model. Devices of this tier have UPS management interfaces, so it makes sense to tie those in to SNMP and email alerts. I like to back ...


8

ZFS by SUN (also part of OpenSolaris; Apples OSX - currently read only) not only does raid with various levels but always check to see if the data written to disk is actually there. consistency is key! RAID is useless if you can´t rely on its integrity. Pick a decent RAID controller (I prefer HP´s) and scrub your RAID to find errors periodically. ...


8

Always. Disks are cheap, your information is not. But use software RAID, so you have the flexibility to move forward or change hardware later on (trust me, you will need it). And also use a checksumming filesystem like ZFS, to protect against silent data corruption (which is very likely with large disks nowadays).


8

When the cost of the redundancy is higher then the cost of being down while what ever is broken is being replaced, it's to much redundancy.


8

I know you have an accepted answer from David, but I'd like to propose a different approach here and share some of my experiences. I've found the problem with using bind_policy soft is that if you don't get a response from the server right away, say for example it is busy or you have high network load, you'll get an LDAP failure immediately. For nss_ldap ...


8

DNS round robin is not a good substitute for a load balancer. The DNS server will continue to hand out the IP of the node that is down, so some of your users will get to your service and some of them will not. When the client makes the DNS query, the DNS server returns all of the IP addresses associated with that name. The magic is done by the DNS server ...


7

For those of you saying you won't use hardware RAID because if the controller fails and you can't get an identcial replacement your screwed, you're going about it the wrong way. If uptime is that critical to you, you should NOT be buying cheap hardware. As was said before, use a good raid controller, HP, LSI, Dell etc. If the controller was purchased from ...


7

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? No you will lose data stored on whole LVM 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 ...


7

On AWS, using GlusterFS with an Elastic Load Balancer and auto scaling EC2 instances should achieve what you want. I can't comment about any other IaaS. Amazon does provide some of what you need to achieve your objective - and allows you to implement the rest. Amazon's EC2 servers are essentially VPSes - you can setup Heartbeat/Corosync/Pacemaker, etc on ...


7

I would simply recommend maintaining two separate clusters and handling replication at the virtual machine level with the vSphere Replication product. This is available to you with your vSphere Essentials Plus license and allows you to maintain an RPO between 15 minutes and 24 hours (adjustable per-VM), as well as the ability to replicate to dissimilar ...


6

You have several choices. We use replication to have several LDAP servers on the network, hidden behind a load balancer, so if one goes down, we still have one available. We use keepalived for our load balancing. You can also use keepalived in a failover setup, where you have a hot backup slave. Secondly, you can have a local LDAP server on each ...



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