outsource from india chennai india programmers freelance php coder freelance outsource scripts programming complicated perl patterns php module installation
outsource from india perl installation and configuration php installation linux system administration US$15,US$19,US$11,US$10 cheap programmer
india outsource outsource india chennai india programmers php perl mysql freelance freelance programmer
SHOWCASE of php and perl scripts CONTACT US for php custom perl scripts
HOME
 
FreeBSD Handbook
Prev Chapter 13 The Vinum Volume Manager Next

13.4 Data Integrity

The final problem with current disks is that they are unreliable. Although disk drive reliability has increased tremendously over the last few years, they are still the most likely core component of a server to fail. When they do, the results can be catastrophic: replacing a failed disk drive and restoring data to it can take days.

The traditional way to approach this problem has been mirroring, keeping two copies of the data on different physical hardware. Since the advent of the RAID levels, this technique has also been called RAID level 1 or RAID-1. Any write to the volume writes to both locations; a read can be satisfied from either, so if one drive fails, the data is still available on the other drive.

Mirroring has two problems:

  • The price. It requires twice as much disk storage as a non-redundant solution.

  • The performance impact. Writes must be performed to both drives, so they take up twice the bandwidth of a non-mirrored volume. Reads do not suffer from a performance penalty: it even looks as if they are faster.

An alternative solution is parity, implemented in the RAID levels 2, 3, 4 and 5. Of these, RAID-5 is the most interesting. As implemented in Vinum, it is a variant on a striped organization which dedicates one block of each stripe to parity of the other blocks. As implemented by Vinum, a RAID-5 plex is similar to a striped plex, except that it implements RAID-5 by including a parity block in each stripe. As required by RAID-5, the location of this parity block changes from one stripe to the next. The numbers in the data blocks indicate the relative block numbers.

Figure 13-3. RAID-5 Organization



Compared to mirroring, RAID-5 has the advantage of requiring significantly less storage space. Read access is similar to that of striped organizations, but write access is significantly slower, approximately 25% of the read performance. If one drive fails, the array can continue to operate in degraded mode: a read from one of the remaining accessible drives continues normally, but a read from the failed drive is recalculated from the corresponding block from all the remaining drives.

Prev Home Next
Access Bottlenecks Up Vinum Objects

This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.

For questions about FreeBSD, read the documentation before contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.
FreeBSD Handbook
FreeBSD Handbook
The FreeBSD Documentation Project
Copyright © 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2007, 2006, 2007 The FreeBSD Documentation Project

Redistribution and use in source (SGML DocBook) and 'compiled' forms (SGML, HTML, PDF, PostScript, RTF and so forth) with or without modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code (SGML DocBook) must retain the above copyright notice, this list of conditions and the following disclaimer as the first lines of this file unmodified.

  2. Redistributions in compiled form (transformed to other DTDs, converted to PDF, PostScript, RTF and other formats) must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

Important: THIS DOCUMENTATION IS PROVIDED BY THE FREEBSD DOCUMENTATION PROJECT "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FREEBSD DOCUMENTATION PROJECT BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS DOCUMENTATION, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

FreeBSD is a registered trademark of Wind River Systems, Inc. This is expected to change soon.

3Com and HomeConnect are registered trademarks of 3Com Corporation.

3ware and Escalade are registered trademarks of 3ware Inc.

ARM is a registered trademark of ARM Limited.

Adaptec is a registered trademark of Adaptec, Inc.

Adobe, Acrobat, Acrobat Reader, and PostScript are either registered trademarks or trademarks of Adobe Systems Incorporated in the United States and/or other countries.

Apple, FireWire, Mac, Macintosh, Mac OS, Quicktime, and TrueType are trademarks of Apple Computer, Inc., registered in the United States and other countries.

Corel and WordPerfect are trademarks or registered trademarks of Corel Corporation and/or its subsidiaries in Canada, the United States and/or other countries.

Sound Blaster is a trademark of Creative Technology Ltd. in the United States and/or other countries.

Heidelberg, Helvetica, Palatino, and Times Roman are either registered trademarks or trademarks of Heidelberger Druckmaschinen AG in the U.S. and other countries.

IBM, AIX, EtherJet, Netfinity, OS/2, PowerPC, PS/2, S/390, and ThinkPad are trademarks of International Business Machines Corporation in the United States, other countries, or both.

IEEE, POSIX, and 802 are registered trademarks of Institute of Electrical and Electronics Engineers, Inc. in the United States.

Intel, Celeron, EtherExpress, i386, i486, Itanium, Pentium, and Xeon are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States and other countries.

Intuit and Quicken are registered trademarks and/or registered service marks of Intuit Inc., or one of its subsidiaries, in the United States and other countries.

Linux is a registered trademark of Linus Torvalds in the United States.

LSI Logic, AcceleRAID, eXtremeRAID, MegaRAID and Mylex are trademarks or registered trademarks of LSI Logic Corp.

M-Systems and DiskOnChip are trademarks or registered trademarks of M-Systems Flash Disk Pioneers, Ltd.

Macromedia, Flash, and Shockwave are trademarks or registered trademarks of Macromedia, Inc. in the United States and/or other countries.

Microsoft, FrontPage, MS-DOS, Outlook, Windows, Windows Media, and Windows NT are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries.

Netscape and the Netscape Navigator are registered trademarks of Netscape Communications Corporation in the U.S. and other countries.

Motif, OSF/1, and UNIX are registered trademarks and IT DialTone and The Open Group are trademarks of The Open Group in the United States and other countries.

Oracle is a registered trademark of Oracle Corporation.

PowerQuest and PartitionMagic are registered trademarks of PowerQuest Corporation in the United States and/or other countries.

RealNetworks, RealPlayer, and RealAudio are the registered trademarks of RealNetworks, Inc.

Red Hat, RPM, are trademarks or registered trademarks of Red Hat, Inc. in the United States and other countries.

SAP, R/3, and mySAP are trademarks or registered trademarks of SAP AG in Germany and in several other countries all over the world.

Sun, Sun Microsystems, Java, Java Virtual Machine, JavaServer Pages, JDK, JSP, JVM, Netra, Solaris, StarOffice, Sun Blade, Sun Enterprise, Sun Fire, SunOS, and Ultra are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and other countries.

Symantec and Ghost are registered trademarks of Symantec Corporation in the United States and other countries.

MATLAB is a registered trademark of The MathWorks, Inc.

SpeedTouch is a trademark of Thomson

U.S. Robotics and Sportster are registered trademarks of U.S. Robotics Corporation.

VMware is a trademark of VMware, Inc.

Waterloo Maple and Maple are trademarks or registered trademarks of Waterloo Maple Inc.

Mathematica is a registered trademark of Wolfram Research, Inc.

XFree86 is a trademark of The XFree86 Project, Inc.

Ogg Vorbis and Xiph.Org are trademarks of Xiph.Org.

Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this document, and the FreeBSD Project was aware of the trademark claim, the designations have been followed by the ``™'' or the ``®'' symbol.

  Home  

This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.

For questions about FreeBSD, read the documentation before contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.

   Web Design Copyright © 1999-2007. Website designed and Webdeveloped and Website programmed by Web developers and Software programmers. We do excellent webdevelopment and software development in asp and .net c# csharp also. Chrisranjana Software Solutions Pvt Ltd. syndicate rss feed