posted by Andrew Schulman on Wed 13th Apr 2005 19:46 UTC

"EVMS, Page 2/3"
A Choice of Interfaces

Once you're finally ready to start using EVMS, you have a choice of three interfaces: command-line, full-screen text using ncurses, and a GUI using GTK. All three interfaces offer essentially the same set of commands and capabilities, and the text and graphical interfaces are laid out identically, so once you learn one it's easy to use the others.

EVMS GUI screenshot

EVMS text interface screenshot

The GUI is easiest to navigate, so I recommend that you use it while you learn your way around EVMS. But the text interface is a valuable middle ground between the GUI and command line, especially for performing system management tasks, where an X server is usually not available. Some disk operations will require you to drop down to single-user mode, and here the text interface is welcome and comfortable. As another example, I've built a custom rescue CD for my file server. The CD has to include EVMS capability, and it doesn't include X. So here again the text interface is welcome.

The command-line interface is intended for scripting, according to the EVMS documentation. But I won't get anywhere near that. EVMS is very good about preventing you from making stupid mistakes, but if you tell it to obliterate a file system on the wrong partition, it will. In the text and graphical interfaces you'll get some feedback and a last chance to bail; but write some wrong logic into a script, and you can destroy a lot of data in a very short amount of time.

Starting to Use EVMS

When you first start to use EVMS, it can be a little overwhelming. One reason is that the authors have developed a whole new set of terminology for all of the many types of storage objects that EVMS uses, in order to avoid confusion with terms used, sometimes inconsistently, by other disk management software. For example, instead of partitions, EVMS uses a somewhat more general notion of disk segments. Logical volumes and volume groups, from Linux' Logical Volume Manager (LVM), become regions and containers. The new terminology is all clearly explained and related to the more familiar ideas, right at the start of the EVMS manual. Still, it takes time to master.

Another hurdle is the large number of tabs in the GUI. EVMS GUI tabs At first it's hard to know where to look, and where to perform the operations you want to perform. This is probably unavoidable; it's a result of the complexity and power of EVMS. One thing that helped me when I finally noticed it is that the highest level objects (volumes: the block devices that you build file systems on) are at the left, and as you move toward the right you move to lower level objects, until you arrive at disks, which (thankfully) correspond to physical disk drives.

All of this detail was confusing to me at first. But I practiced using the GUI to create and destroy objects in some spare disk space; related the objects in the GUI to old familiar concepts from LVM; reread the manual; and spent some time looking at the sample diagram. After a while, it all became clear.

Power Grows on You

Did you know that it's possible to move the data in a live file system from one disk partition to another? That's right: you can move a file system while leaving it mounted for reading and writing. At least, you can if your file system is built on an LVM or LVM2 logical volume. EVMS knows which types of volumes support this operation, and allows you to do it when they do.

Did you know that you can expand some file systems without dismounting them? Not all file systems support this, but when they do, EVMS allows you to do it. ReiserFS, for example, provides the capability to expand a mounted file system, and EVMS knows it and allows you to use it.

These examples illustrate the core strength of EVMS: it ties together the capabilities that are already available in many different tools, into a coherent framework accessible through a single, consistent interface. It also makes disk management easier, by taking care of the details. And it makes disk management safer, by knowing what operations you can't or shouldn't do, and not allowing you to do them.

Here's another example. Have you ever had to shrink a disk partition and the file system that lived on it? If you haven't, take it from me: it requires great care and carries a high risk of destroying your data. You have to shrink first the file system and then the partition, paying careful attention that the numbers and sizes of blocks are the same in both operations. Different commands are required to resize the partition and each type of file system, with different options, and sometimes different default block sizes. Issue a wrong command, and your data is history. This is exactly the sort of dangerous and error-prone task that software should handle for us, and EVMS does. Just tell it to shrink (or expand) a volume, and it takes care of the details. The task is both easier and safer.

Table of contents
  1. "EVMS, Page 1/3"
  2. "EVMS, Page 2/3"
  3. "EVMS, Page 3/3"
e p (0)    11 Comment(s)

Technology White Papers

See More