Virtual Servers(2)

Virtualized servers do all the good and bad things regular servers do. They boot up, power down, suspend, hang, and even crash. If a guest OS or a device driver it uses is buggy, the virtual PC will crater. But not the physical computer, and that's key.

If your OS crashes or an application hangs, or even if you install a software fix that requires a reboot, nothing happens to the hardware. One virtual machine can fail over to another in a purely virtual sense or in a way that's closer to the real thing. Even if certain hardware devices have malfunctioned, so long as the fail-over target is configured to use a secondary network adapter and an alternate path to storage, the fail-over will work exactly as it would if the virtual PCs were physical PCs.

In most cases, an enterprise management system will monitor and react to a virtual fail-over as if it were the real thing. Solutions such as HP OpenView see and interact with virtual servers the same way they do with physical ones. The reported configurations of the servers will change after they're virtualized, but it's entirely likely that the day-to-day management of your shop will experience little change.

In addition, most virtualization systems bundle solution-specific management software, allowing an administrator to sit at a central console and manipulate all the virtual servers in an enterprise. It's quite an eye-opener to swap out a virtual Ethernet card without ever touching the hardware.

A virtualization solution's management console gives you a degree of control over your virtual PCs that surpasses what administrators can do with traditional tools. From a central location, you can boot and shut down virtual PCs as needed. It's also possible to pause them, which harmlessly freezes them in their current state, or hibernate them, putting them in a deep freeze by saving their state to a file on disk. By overwriting the disk file, you can restore PCs from a backed-up state and roll back changes that rendered the guest inoperable, all from a terminal session.

In environments with a mix of operating systems——a common condition that turns even simple consolidation into a messy affair—— one solution would be to host each OS in its own VM. For example, on a PC server running one of VMware's virtualization solutions, you can run any combination of Windows 2003 Server, Windows 2000, Windows NT 4.0, various flavors of Linux, and FreeBSD. You can even use VMs to host different versions of the same OS. Linux software is infamous for dependence on specific versions and vendor distributions of Linux. Virtualization is the only way to run applications designed for Red Hat 7.2 and Suse 9.0 simultaneously on a single server.

Virtualization is magnificent stuff, but it doesn't cure all ills. You can never create a virtual PC that outperforms the physical system underneath. You will learn much about your applications' system requirements from moving them to a virtual environment. They'll likely surprise you, either with how little of the original server they used——that's the typical case——or how piggish they are. If necessary, you can throttle the nasty ones down.

And while one of the great benefits of virtualization is security——it's hard to accomplish much by cracking a system that doesn't exist——a virtualized PC can still be compromised. Fortunately, the cure is to overwrite the virtual PC's disk image with one that's known to be clean, but managing virtual servers still requires vigilance.

Ultimately, hardware consolidation is only one reason to opt for server virtualization, and it has wide appeal. Still, depending on each department's unique needs, IT managers are sure to find innumerable ways that virtualization can benefit your enterprise. (The End)

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虛擬服務(wù)器 (2)

虛擬化的服務(wù)器會(huì)做正常服務(wù)器會(huì)做的所有好事和壞事。它們會(huì)自舉、宕機(jī)、掛起、暫停、甚至崩潰。如果它的客 OS或者設(shè)備驅(qū)動(dòng)程序有錯(cuò)誤，虛擬PC機(jī)將崩潰。而物理的計(jì)算機(jī)不會(huì)那樣，這是關(guān)鍵。

如果 OS崩潰或者應(yīng)用程序暫停，甚至如果你安裝需要重新引導(dǎo)的軟件補(bǔ)丁，對(duì)硬件不會(huì)發(fā)生任何影響。一臺(tái)虛擬機(jī)能以完全虛擬的方式或者以更近似于真實(shí)的方式，將故障轉(zhuǎn)移到另一臺(tái)虛擬機(jī)。即便某個(gè)硬件裝置有故障，只要配置好故障轉(zhuǎn)移的目標(biāo)，能使用第二網(wǎng)卡和到存儲(chǔ)設(shè)備的替代通道，故障轉(zhuǎn)移就能正確地工作，如同虛擬機(jī)就是一臺(tái)物理PC機(jī)那樣地工作。

在多數(shù)情況下，企業(yè)管理系統(tǒng)將對(duì)虛擬的故障轉(zhuǎn)移進(jìn)行監(jiān)視和做出反應(yīng)，好像就是真實(shí)的東西。諸如 HP OpenView一類的解決方案對(duì)虛擬服務(wù)器做出的反應(yīng)和對(duì)物理服務(wù)器做出的反應(yīng)是一樣的。在虛擬化之后，報(bào)告的服務(wù)器配置將改變，但是整體上，數(shù)據(jù)中心日常管理幾乎沒有什么變化。

此外，多數(shù)虛擬化系統(tǒng)與特定的解決方案管理軟件是捆綁在一起的，允許管理員坐在中央控制臺(tái)，管理整個(gè)企業(yè)的所有虛擬服務(wù)器。在不用碰硬件的情況下，就能置換以太網(wǎng)卡，真讓人大開眼界。

虛擬化解決方案的管理控制臺(tái)讓你一定程度上控制虛擬 PC機(jī)，這種控制程度超過了用傳統(tǒng)工具能做到的程度。從一個(gè)集中點(diǎn)，就能按需要引導(dǎo)和關(guān)閉虛擬PC機(jī)。也能暫停它們，無害地將它們凍結(jié)在當(dāng)前的狀態(tài)，或者使它們休眠，通過將它們的狀態(tài)保存到磁盤上的一個(gè)文件中，將它們深度凍結(jié)。通過重寫該磁盤文件，就能將PC機(jī)從備份狀態(tài)中恢復(fù)過來，從最后一次會(huì)話開始將使之不工作的改變?nèi)炕貪L。

在多種操作系統(tǒng)混用的環(huán)境下(這是一種常見的情況，會(huì)把簡(jiǎn)單的服務(wù)器集中弄得亂七八糟)，一種解決辦法就是將每個(gè) OS在各自虛擬機(jī)上運(yùn)行。例如，在一臺(tái)運(yùn)行VMware虛擬方案的PC服務(wù)器上，你能運(yùn)行Windows 2003 Server、 Windows 2000、 Windows NT 4.0、各種版本的Linux以及FreeBSD的各種組合。甚至能運(yùn)行同一OS的不同版本。Linux因?qū)μ囟ò姹竞蛷S商有依賴性而搞得名聲狼藉。虛擬化是惟一的方法，讓一臺(tái)服務(wù)器上同時(shí)運(yùn)行為Red Hat 7.2 和Suse 9.0設(shè)計(jì)的應(yīng)用程序。

虛擬化是個(gè)好東西，但它不能包治百病。你永遠(yuǎn)不能建立一個(gè)虛擬 PC機(jī)，其性能超過它所在的物理系統(tǒng)。將應(yīng)用程序移到虛擬環(huán)境，你能從中學(xué)到很多應(yīng)用程序的系統(tǒng)要求。它們可能讓你吃驚，不是它們只用了原來服務(wù)器非常少的一部分(這是一種很典型的情況)，就是它們是多么的貪婪。如果有必要，你就能關(guān)閉那些討厭的程序。

虛擬化最大的好處之一是安全(破壞實(shí)際不存在的系統(tǒng)是難以實(shí)現(xiàn)的)，同時(shí)虛擬化的 PC機(jī)還能做出妥協(xié)。辦法是把虛擬PC機(jī)的磁盤映像重寫到已知是干凈的磁盤上，但是管理虛擬服務(wù)器仍需要警惕。

歸根結(jié)底，硬件集中不是選擇服務(wù)器虛擬化的惟一理由，它還有很廣泛的需求。依據(jù)每個(gè)部門不同的要求， IT 管理人員一定能找到數(shù)不清的方法，讓虛擬化為企業(yè)服務(wù)。