When you write data, it doesn’t necessarily get written to disk right then. The kernel maintains caches of many things, and disk data is something where a lot of work is done to keep everything fast and efficient. That’s great for performance, but sometimes you want to know that data really has gotten to the disk drive. This could be because you want to test the performance of the drive, but could also be when you suspect a drive is malfunctioning: if you just write and read back, you’ll be reading from cache, not from actual disk platters.

So how can you be sure you are reading data from the disk? The answer actually gets a little complicated, particularly if you are testing for integrity, so bear with me.

Obviously the first thing you need to do is get the data in the cache sent on its way to the disk. That’s “sync”, which tells the kernel that you want the data written. But that doesn’t mean that a subsequent read comes from disk: if the requested data is still in cache, that’s where it will be fetched from. It also doesn’t necessarily mean that the kernel actually has sent the data along to the disk controller: a “sync” is a request, not a command that says “stop everything else you are doing and write your whole buffer cache to disk right now!”. No, “sync” just means that the cache will be written, as and when the kernel has time to do so.

Traditonally, the only way to be sure you were not reading back from the cache was to overwrite the cache with other data. That required two things: knowing how big the cache is at this moment, and having unrelated data of sufficient size to overwrite with.

On older Unixes with fixed sized buffer caches, the first part was easy enough, and since memory was often expensive and in shorter supply than it is now, the cache wasn’t apt to be all that large anyway. That’s changed radically: modern systems allocate cache memory dynamically and while the total cache is still small compared to disk drives, it can now be gigabytes of data that you need to overwrite. http://www.zerivista.com

Written by azerivista.com Miller.

A few people would perhaps say MacOS X is the best. Windows, of course, is not the one geeks want to be associated with.

One more OS is making waves in the academia and business world and with serious geeks for the last yr or so, after it was open sourced. For all the right reasons. That is the grand daddy of all, the most popular Unix - Solaris OS. No other operating system, not even Linux can claim to have as much geeky meat as Solaris. Some of the mouth watering stuff in Solaris 10, especially for geeks include: Zones - software virtualization feature which has no match in any other OS. I can’t remember which technology in any other OS comes even close. BSD jails, perhaps.

ZFS - the ultra modern file system, again with no match. The only thing that comes close is VxFS but ZFS is free with source code in the open.

DTrace - again no match anywhere. The capability to look into each and every place into the kernel and other parts in a running system using DTrace is unparalleled. It has been winning accolades all over. SystemTap for Linux is still not complete and its design makes it unlikely to be able to compete with DTrace in the future.

BrandZ - It gives you the capability to run Linux apps on top of Solaris. For example, you can run a version of Linux like CentOS right inside a Solaris Zone. Say you want to play Quake or use Google Earth which don’t have Solaris apps; just create a Zone in Solaris, install your Linux in the zone and play away with the apps which are available in Linux. How more geeky can one get!

Of course, serious business won’t play games. For them there are other more serious features like:
Fault Management Architecture (FMA), Service Management Framework(SMF), etc.

Linux is a good Operating System and has the advantage of having more drivers. But in almost everything else, Solaris scores higher. Now that it is open sourced it should get people interested in creating drivers. The community and codebase of Solaris is called OpenSolaris. Looking at the number of posts and projects there, it really looks like a dynamic and vibrant group of geeks.

Written by blogginginvestor.

On the contrary, the industry experts are most impressed by its power and richness and more and more users are embracing Linux. Changing operating systems is definitely a big labor but this one-time labor is nothing if compared to all that one does to tackle those terrible blue screens of death, frozen windows, system crashes, viruses, data loss and spy wares. We are not destined to spend a quarter of our lives installing, de-installing and re-installing anti-virus tools or restarting computers and those geeks and non-geeks, who realize this, close their Windows, migrate to Linux and live happily ever after. And, I’ll give you just some of the reasons why.

1. FREEDOM: The number one reason why Linux is the choice of many is the freedom it gives. It “let’s you do everything you want to do” but this is not the only aspect of this freedom. Linux liberates you from the yoke of vendors who hurl unwanted updates your way, and frees you from the sight of the horrible blue screens of death and its likes. This precious freedom doesn’t cost you a penny. You can download a free distribution of Linux from the internet. Otherwise, you can get a CD from the market after spending a minimal amount of money and without worrying about the licensing fees or about violating the piracy laws because Linux is open source and it comes with GNU General Public License. This is its true beauty and the reason why Linus Torvalds and the whole Linux community, working to make things better, have many admirers.

2. STABILITY:

With Linux, your computer doesn’t freeze or slow down because of memory leaks. It has a high performance level and can run for years without causing you trouble. This actually means complete control as you will not find yourself pushing Ctrl+Alt+Del keys in sheer desperation. Problems pop up only when any of the hardware fails. Its excellent stability is another reason which attracts users.

3. SECURITY:

No OS can beat Linux when it comes to security. It’s a long debated issue and something which bothers Microsoft so much so it started its own campaign to make people believe Linux is not any safer but Linux users are already aware of the vulnerabilities of Windows and know Linux differs when it comes to it and can easily be termed as the most secure operating system. The design of Linux is different from that of Windows. This doesn’t make it an easy target and even if half of the world switches to Linux, the attacks will not cause much damage even though the source code of Linux is available for every Tom, Dick and Harry. The availability of the source code only means advantage. Millions of programmers have contributed to beef up the security of Linux. Bugs are fixed just as soon as they are identified. Linux is getting better and better every passing day. For a comprehensive report on the security of Linux as compared to windows, you can visit:
http://www.theregister.co.uk/security/security_report_windows_vs_linux/

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