Somewhere out there!

I’ve been looking at various storage options recently. DRBD is pretty cool:

And, of course, we only will resynchronize those parts of the device that actually have been changed. DRBD has always done intelligent resynchronization when possible. Starting with the DBRD-0.7 series, you can define an “active set” of a certain size. This makes it possible to have a total resync time of 1–3 min, regardless of device size (currently up to 4TB), even after a hard crash of an active node.

DRBD is a network block level intelligent replication protocol. It syncs local disk blocks on two separate nodes and smartly manages dirty blocks while out of communication. Normally this is used for Active/Passive or Active/Active cluster HA. It could also provide a method for off site replication.

Run a storage server with iSCSI or AoE targets on LVM devices over the DRDb block device, with the secondary node on a remote server via a vpn. Specific details about this setup are discussed in Disaster Recovery with “Tele-DRBD” on the Linux HA Wiki. Some details on LVM over DRBD. Also worth checking the NFS on DRBD page.

Technorati Tags: drbd, ha, replication, storage

VMWare bases the MAC address of interface on it’s internal UUID. If you shift a machine (copy, rename) vmware asks to update the UUID. You might get something like this:

# ifup eth0
SIOCSIFADDR: No such device
eth0: ERROR while getting interface flags: No such device
SIOCSIFADDR: No such device
SIOCSIFADDR: No such device
eth0: ERROR while getting interface flags: No such device
eth0: ERROR while getting interface flags: No such device

The solution found by hbraga is to check /etc/iftab. Ubuntu on install adds the MAC address for each interface to this file. Either comment out the lines or update them to reflect the correct details.

Technorati Tags: vmware, ubuntu, network error fix

AnandTech: Server Guide part 2

Even the so called “Nearline” (Seagate) or “Raid Edition” (RE, Western Digital) SATA drives which are made to operate in enterprise storage racks, and which are more reliable than desktop disks, are not made for the mission critical, random transactional applications. Their MTBF (Mean Time Between Failure) is still at least 20% lower than typical enterprise disks, and they will show the similar failure rates when used with highly random server workloads as desktop drives.Also, the current SATA drives on average experience an Unrecoverable Error every 12.5 terabytes written or read (EUR of 1 in 1014 bits). Thanks to the sophisticated drive electronics, SAS/SCSI disks experience these kinds of errors 100 (!) times less. It would seem that EUR numbers are so small that they are completely negligible, but consider the situation where one of your hard drives fails in a RAID-5 or 6 configuration. Rebuilding a RAID-5 array with five 200 GB SATA drives results in reading 0.8 terabytes and writing 0.2 terabytes, in total 1 terabytes. So you have 1/12.5 or 8% chance of getting an EUR on this SATA array. If we look at a similar SCSI enterprise array, we would get a 0.08% chance on one unrecoverable error. It is clear an 8% chance of getting data loss is a pretty bad gamble for a mission critical application.

Another good point that Seagate made in the same study concerns vibration. When a lot of disk spindles and actuators are performing a lot of very random I/O operations in a big storage rack, quite a bit of rotational vibration is the result. In the best case the actuator will have to take a bit more time to get to the right sector (higher seek time) but in the worst case the read operation has to be retried. This can only be detected by the software driver, which means that the performance of the disk will be very low. Enterprise disks can take about 50% more vibration than SATA desktop drives before 50% higher seek times kill the random disk performance.

Technorati Tags: hardware, storage

AnandTech: Server Guide Part 1

There are two big problems with the “hardware choice does not matter much” kind of reasoning. The first is that the TCA is still a big part of the total TCO. For example this study[1] estimates that the price of buying the server is still about 40-50% of the TCO, while maintenance comprises a bit more than 10% and operation costs take about 40% of TCO pie. Thus we can’t help but be wary when a vendor claims that a high price is okay, because the maintenance on his product is so much lower than the competition.Secondly, certain hardware choices have an enormous impact on the rest of the TCO picture. One example is hot-spare and hot-swappable RAID arrays which on average significantly reduce the time that a server is unreachable. This will also become clearer as we dig deeper into the different hardware features of modern servers and the choices you will have to make.

RAS features

Studies done by IBM say that about 50% of the hardware failures are related to hard disk problems and 25% are due to a power supply failure. Fans with 8% are a distant third, so it is clear you need power supplies and hard disks of high reliability, the R of RAS.

Technorati Tags: hardware, server

AnandTech: Quad Core Intel Xeon 53xx Clovertown

This means that we have to subtract about 13% of the performance figures if we want to keep the TDP the same, and in that case some of the “compelling gains” are no longer really tangible. So we can conclude that CRM, Financial analysis, ERP and Java applications are the best applications for our Clovertown Xeon. For rendering, transaction processing, and especially structural simulation (LS Dyna) and flow modeling (fluent) the picture is a lot less clear.

 …

To the financial analysts, CRM, ERP and Java server people, the new quad core Xeon E53xx is close to irresistible. You can get four cores for the price of two, or up to eight (!) cores in a relatively cheap dual socket server. We observed at least a 40% performance increase compared to probably the best dual core CPU of today: the Xeon 5160.

For the people looking for a 3D rendering workstation, your usage model will determine whether the Xeon 5160 or the Xeon E5345 is the best solution. You get better animation and 3D manipulation performance (mostly single threaded) and better rendering performance at resolutions lower than High Definition with the Xeon 5160. 3D render servers are better off with the Quad Xeon E53xx but only if they have to render at 720p or full HD (1080p) resolutions.

The past 6 months have been excellent for Intel: after regaining the performance crown in the dual socket server market, there is also now a very viable and lowly priced alternative for the more expensive quad Opteron based systems. However, it is not all bad news for AMD. The current quad core might be good for Intel’s yields, time to market, and production costs, but it does have a weakness. The quad core Xeon scaling is very mediocre, and this despite a high performance chipset. The current 5000p chipset has a large 16MB snoop filter, reads speculatively to decrease memory latency, and has a whole other bag of clever tricks to get more performance out of the platform. Despite all this and a 2x4MB L2 cache setup, the quad core Xeon scales worse than the relatively old quad Opteron platform.

Technorati Tags: hardware, intel, opteron, review

This is pretty clever: Running Windows on the Amazon Elastic Compute Cloud with Qemu and Linux.

Technorati Tags: ec, qemu, windows

rPath is some thing I’ve been meaning to learn about for a while. I particularly like their view on the future of software and virtualisation, which is similar to my view of software appliances.

Linux.com | Talking virtualization with rPath
Another trend that Adams expects to become clearer by the end of 2007 is a concern about how to manage virtual applications. As virtual applications come into wider use, Adams suggests, “the normal cycle of supply and demand will actually result in everyone consuming more software.” If that happens, then the question becomes, “What sort of characteristics does a virtual appliance need to be more maintainable, more manageable?”

Traditionally, software vendors have assumed that management of their products is the customers’ concerns. However, as virtualization takes hold, Adams expects to see vendors as starting to offer managed services. “One of our hypotheses about what virtual appliances can do is freeing the end user from worrying about the IT stack, operating system, and other issues, because they’re essentially black box and having the software provide all that, which shifts responsibility and control” Adams says. “Now, [if that happens] you have to ask: ‘If I were a software vendor, what would I need?'”

Manageability is one of the aspects that I think will drive the uptake of Software Appliances. Virtualisations creates the platform to allow the outsourcing of application management to those best suited to handle, while allowing the client to retain ownership of their data and enviroment.

Technorati Tags: virtualisation, software appliances, rpath

From GANB.

Since wordpress.com wasn’t an option due to the CNAME issues, I’ve shifted the blog to Dreamhost. I’ve got a Dreamhost account for other things, but it will serve well enough for this blog allowing me to retire one of my virtual machines.

My old theme was using some old functions which are now broken, so I’m temporarily using the default WordPress theme. However it seems to be broken for the index page. I’ve been meaning to update my theme for a while, but never find the time.  Probably have to sort it out later, seems to be a bug in the sidebar.php.

I’m thinking of moving to wordpress.com so I can ignore the monthly hassle of upgrading WordPress avoid any security issues. Particularily when I’m out of town this is a PITA.