Re: toh - backup coverage calculation
Hiran Chaudhuri <[email protected]> Sat, 12 Jan 2013 13:53:44 +0100
| Newsgroups | gmane.comp.sysutils.backup.sarab |
|---|---|
| Message-ID | <[email protected]> |
--===============1783617647346955452== Content-Type: multipart/alternative; boundary="----FL4SD53VKDM77NXQMAB1J2KQLF1OHT" ------FL4SD53VKDM77NXQMAB1J2KQLF1OHT Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Hi Lars. Sorry for the late answer, but finally I found the time to think = about the formula I inherited with the project. You are right, and I will u= pdate the documentation as soon as I get to it. Hiran LM <hermes.tris= [email protected]> schrieb: Hi Hiran, the difference are the brackets. Firs= t you have to substract one from n, than you have to raise 2 by the result:= 2^(n-1) Lars Am Sunday, 9. December 2012 15:22 schrieb Hiran Chaudhuri:= > Hi Lars. > > Now you are confusing me. While I've never worried about t= he formula, it might be worth thinking about it. > > On the other hand wit= h your correction you exactly state what is said on the web page. So where = is the difference? > > Hiran > > > > > LM <[email protected]>= schrieb: > > > Am Saturday, 8. December 2012 16:54 schrieb LM: > > Hi, >= > > > I have a question regarding the backup coverage calculation (FAQ #1= - http://sarab.sourceforge.net/faq.php#1) > > > > >1. What are the benefi= ts of using the Towers of Hanoi backup rotation strategy? > > > > > To cal= culate 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-tapes, and subtract 1. F= or 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, nearly three years! This rota= tion 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 calculation? With 10 virtu= al 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 num= ber of virtual-tapes? > > > > Best, > > Lars > > > > Maybe the formula s= hould be 2^(n-1). Raise 2 to the number of virtual-tapes? > > Sorry, I mea= nt: Raise 2 to the number of virtual-tapes minus 1 > >____________________= _________________________ > > LogMeIn Rescue: Anywhere, Anytime Remote su= pport for IT. Free Trial > Remotely access PCs and mobile devices and provi= de 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 >____________________________________= _________ > > SaraB-discuss mailing list > [email protected]= e.net > https://lists.sourceforge.net/lists/listinfo/sarab-discuss > > _= ____________________________________________ LogMeIn Rescue: Anywhere, Any= time Remote support for IT. Free Trial Remotely access PCs and mobile devic= es and provide instant support Improve your efficiency, and focus on delive= ring more value-add services Discover what IT Professionals Know. Rescue de= livers http://p.sf.net/sfu/logmein_12329d2d _______________________________= ______________ SaraB-discuss mailing list [email protected].= net https://lists.sourceforge.net/lists/listinfo/sarab-discuss ------FL4SD53VKDM77NXQMAB1J2KQLF1OHT Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable <html><head></head><body>Hi Lars.<br> <br> Sorry for the late answer, but f= inally I found the time to think about the formula I inherited with the pro= ject.<br> You are right, and I will update the documentation as soon as I g= et to it.<br> <br> Hiran<br> <br> <br><br><div class=3D"gmail_quote"><br> <= br> LM <[email protected]> schrieb:<blockquote class=3D"gmai= l_quote" style=3D"margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204= , 204, 204); padding-left: 1ex;"> <pre style=3D"white-space: pre-wrap; word= -wrap:break-word; font-family: sans-serif">Hi Hiran,<br /><br />the differe= nce are the brackets. First you have to substract one from n, than you have= to raise 2 by the result: 2^(n-1)<br /><br />Lars<br /><br /><br />Am Sund= ay, 9. December 2012 15:22 schrieb Hiran Chaudhuri:<br />> Hi Lars.<br /= >> <br />> Now you are confusing me. While I've never worried about t= he formula, it might be worth thinking about it.<br />> <br />> On th= e 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 />> <br />> <br />> LM <[email protected]&= gt; schrieb:<br />> <br />> <br />> Am Saturday, 8. December 2012 = 16:54 schrieb LM:<br />> > Hi,<br />> > <br />> > I have = a question regarding the backup coverage calculation (FAQ #1 - <a href=3D"h= ttp://sarab.sourceforge.net/faq.php#1">http://sarab.sourceforge.net/faq.php= #1</a>)<br />> > <br />> > >1. What are the benefits of usin= g the Towers of Hanoi backup rotation strategy?<br />> > <br />> &= gt; > 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-tapes, an= d subtract 1. For example, five backups would yield a 31-day rotation (2^5-= 1).<br />> > > <br />> > > If you used 10 virtual-tapes w= ith the Towers of Hanoi rotation strategy, you would have backup coverage f= or 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 hold 10 backups: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 days ago. = <br />> > <br />> > Maybe the formula should be 2^(n-1). Raise = 2 to the number of virtual-tapes?<br />> > <br />> > Best,<br /= >> > Lars<br />> <br />> <br />> > Maybe the formula shou= ld 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 />> <br />> LogMeIn Rescue: Anywhere, Anytime Remo= te support for IT. Free Trial<br />> Remotely access PCs and mobile devi= ces and provide instant support<br />> Improve your efficiency, and focu= s on delivering more value-add services<br />> Discover what IT Professi= onals Know. Rescue delivers<br />> <a href=3D"http://p.sf.net/sfu/logmei= n_12329d2d">http://p.sf.net/sfu/logmein_12329d2d</a><br />><hr /><br />&= gt; <br />> SaraB-discuss mailing list<br />> [email protected]= rceforge.net<br />> <a href=3D"https://lists.sourceforge.net/lists/listi= nfo/sarab-discuss">https://lists.sourceforge.net/lists/listinfo/sarab-discu= ss</a><br />> <br />> <br /><br /><hr /><br />LogMeIn Rescue: Anywher= e, Anytime Remote support for IT. Free Trial<br />Remotely access PCs and m= obile devices and provide instant support<br />Improve your efficiency, and= focus on delivering more value-add services<br />Discover what IT Professi= onals Know. Rescue delivers<br /><a href=3D"http://p.sf.net/sfu/logmein_123= 29d2d">http://p.sf.net/sfu/logmein_12329d2d</a><br /><hr /><br />SaraB-disc= uss mailing list<br />[email protected]<br /><a href=3D"h= ttps://lists.sourceforge.net/lists/listinfo/sarab-discuss">https://lists.so= urceforge.net/lists/listinfo/sarab-discuss</a><br /></pre></blockquote></di= v></body></html> ------FL4SD53VKDM77NXQMAB1J2KQLF1OHT-- --===============1783617647346955452== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline ------------------------------------------------------------------------------ Master Visual Studio, SharePoint, SQL, ASP.NET, C# 2012, HTML5, CSS, MVC, Windows 8 Apps, JavaScript and much more. Keep your skills current with LearnDevNow - 3,200 step-by-step video tutorials by Microsoft MVPs and experts. SALE $99.99 this month only -- learn more at: http://p.sf.net/sfu/learnmore_122912 --===============1783617647346955452== 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 --===============1783617647346955452==--