Re: toh - backup coverage calculation
Hiran Chaudhuri <[email protected]> Sun, 09 Dec 2012 15:22:37 +0100
| Newsgroups | gmane.comp.sysutils.backup.sarab |
|---|---|
| Message-ID | <[email protected]> |
--===============0161747594838817437== Content-Type: multipart/alternative; boundary="----HGMAM1P8A9MESXX1153MLDB6SXCX9U" ------HGMAM1P8A9MESXX1153MLDB6SXCX9U Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Hi Lars. Now you are confusing me. While I've never worried about the form= ula, it might be worth thinking about it. On the other hand with your corr= ection you exactly state what is said on the web page. So where is the diff= erence? Hiran LM <[email protected]> schrieb: Am Saturday, = 8. December 2012 16:54 schrieb LM: > Hi, > > I have a question regarding t= he backup coverage calculation (FAQ #1 - http://sarab.sourceforge.net/faq.p= hp#1) > > >1. What are the benefits of using the Towers of Hanoi backup ro= tation strategy? > > > To calculate how long a given number of virtual-tap= es will cover, use the formula 2^n =E2=80=93 1. Raise 2 to the number of vi= rtual-tapes, and subtract 1. For example, five backups would yield a 31-day= rotation (2^5-1). > > > > If you used 10 virtual-tapes with the Towers of= Hanoi rotation strategy, you would have backup coverage for 1023 days, nea= rly three years! This rotation would have backups from 1, 2, 4, 8, 16, 32, = 64, 128, 256, 512 and 1023 days ago. > > Isn't there an error in this calc= ulation? With 10 virtual tapes I can only hold 10 backups: 1, 2, 4, 8, 16, = 32, 64, 128, 256, 512 days ago. > > Maybe the formula should be 2^(n-1). = Raise 2 to the number of virtual-tapes? > > Best, > Lars > Maybe the for= mula should be 2^(n-1). Raise 2 to the number of virtual-tapes? Sorry, I m= eant: Raise 2 to the number of virtual-tapes minus 1 _____________________= ________________________ LogMeIn Rescue: Anywhere, Anytime Remote support = for IT. Free Trial Remotely access PCs and mobile devices and provide insta= nt support Improve your efficiency, and focus on delivering more value-add = services Discover what IT Professionals Know. Rescue delivers http://p.sf.n= et/sfu/logmein_12329d2d _____________________________________________ Sara= B-discuss mailing list [email protected] https://lists.so= urceforge.net/lists/listinfo/sarab-discuss ------HGMAM1P8A9MESXX1153MLDB6SXCX9U Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable <html><head></head><body>Hi Lars.<br> <br> Now you are confusing me. While = I've never worried about the formula, it might be worth thinking about = it.<br> <br> On the other hand with your correction you exactly state what = is said on the web page. So where is the difference?<br> <br> Hiran<br> <br= ><br><div class=3D"gmail_quote"><br> <br> LM <[email protected]= > schrieb:<blockquote class=3D"gmail_quote" style=3D"margin: 0pt 0pt 0pt= 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"> <pr= e style=3D"white-space: pre-wrap; word-wrap:break-word; font-family: sans-s= erif"><br />Am Saturday, 8. December 2012 16:54 schrieb LM:<br />> Hi,<b= r />> <br />> I have a question regarding the backup coverage calcula= tion (FAQ #1 - <a href=3D"http://sarab.sourceforge.net/faq.php#1">http://sa= rab.sourceforge.net/faq.php#1</a>)<br />> <br />> >1. What are the= benefits of using the Towers of Hanoi backup rotation strategy?<br />> = <br />> > To calculate how long a given number of virtual-tapes will = cover, use the formula 2^n =E2=80=93 1. Raise 2 to the number of virtual-ta= pes, and subtract 1. For example, five backups would yield a 31-day rotatio= n (2^5-1).<br />> > <br />> > If you used 10 virtual-tapes with= the Towers of Hanoi rotation strategy, you would have backup coverage for = 1023 days, nearly three years! This rotation would have backups from 1, 2, = 4, 8, 16, 32, 64, 128, 256, 512 and 1023 days ago.<br />> <br />> Isn= 't there an error in this calculation? With 10 virtual tapes I can only hol= d 10 backups: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 days ago. <br />> <b= r />> Maybe the formula should be 2^(n-1). Raise 2 to the number of virt= ual-tapes?<br />> <br />> Best,<br />> Lars<br /><br /><br />> = Maybe the formula should be 2^(n-1). Raise 2 to the number of virtual-tapes= ?<br /><br />Sorry, I meant: Raise 2 to the number of virtual-tapes minus 1= <br /><br /><hr /><br />LogMeIn Rescue: Anywhere, Anytime Remote support fo= r IT. Free Trial<br />Remotely access PCs and mobile devices and provide in= stant support<br />Improve your efficiency, and focus on delivering more va= lue-add services<br />Discover what IT Professionals Know. Rescue delivers<= br /><a href=3D"http://p.sf.net/sfu/logmein_12329d2d">http://p.sf.net/sfu/l= ogmein_12329d2d</a><br /><hr /><br />SaraB-discuss mailing list<br />SaraB-= [email protected]<br /><a href=3D"https://lists.sourceforge.net= /lists/listinfo/sarab-discuss">https://lists.sourceforge.net/lists/listinfo= /sarab-discuss</a><br /></pre></blockquote></div></body></html> ------HGMAM1P8A9MESXX1153MLDB6SXCX9U-- --===============0161747594838817437== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d --===============0161747594838817437== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ SaraB-discuss mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/sarab-discuss --===============0161747594838817437==--