Lee; With a simple stripe, there is no overhead. Striping with parity (involved in, for example, RAID-5) is where you will see overhead, as the parity bits must be stored in addition to the data.
I think what you are noticing is related to the fact that you can't evenly divide 45 by 8. By selecting 8 stripes, you were only getting 40 mod 9s in your LV. 306/45 is within a reasonable error margin of 275/40. I'm willing to bet that after creating the 275 GB, 8-stripe LV, you would've had 31 GB "left over" in your volume group, on which you could have created a second LV (with either 1 stripe or 5 stripes). ok r. > -----Original Message----- > From: Lee Stewart [mailto:[EMAIL PROTECTED] > Sent: Tuesday, August 19, 2008 5:26 PM > To: [email protected] > Subject: Re: Striped LVM max size > > I follow that logic. Since you can't choose 9 (in the SLES10 drop > down), 5 works. Fewer than the "as many stripes as you have volumes" > recommendation... > > But it still leaves my basic question -- how do you know or > plan for what the max size you can use is? > > When we first set it up 45 mod 9s, 306GB, with 8 stripes we > had to hunt > and peck all the way down to 275GB... So 31GB went into > the stripes. > If I wanted a 300GB LVM, how do I know how much raw space I need? > > Thanks, > Lee > > > > Mark Perry wrote: > > Lee Stewart wrote: > > <SNIP> > >> For example, doing an LVM with 45 mod 9s. Round numbers > math gives me > >> 6.8GB/volume x 45 volumes = 306GB. That's close to what > Max gives. > >> But what's the number with 8 stripes? > >> > > > > Hello Lee, > > The idea is to put each of the specified stripes on a > different DASD. > > I have always used a number of stripes that was a factor of > the number > > of DASD in the VG. > > > > So for your example of 45 DASD that would mean using a number of > > stripes of either 9 or 5. > > > > Also I have always added extra DASD to the VG pool in > multiples of the > > number of stripes, in the above example that would mean > adding either > > 9 or 5 DASD at a time. > > > > If you do not do as I suggest, then you can end up with > more stripes > > on one or more DASD than on others. This would defeat the > purpose of > > using stripes, which is to spread the I/O load "evenly" > across multiple DASD. > > > > If you want to use a number of stripes of 8, then either > put 48 DASD > > in your VG pool or reduce to 40. 48 has more factors, so > with 48 DASD > > in the VG you could choose a number of stripes from > 2,3,4,6,8,12,16,24. > > > > mark > > > > > ---------------------------------------------------------------------- > > For LINUX-390 subscribe / signoff / archive access > instructions, send > > email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or > > visit http://www.marist.edu/htbin/wlvindex?LINUX-390 > > > > -- > > Lee Stewart, Senior SE > Sirius Computer Solutions > Phone: (303) 798-2954 > Fax: (720) 228-2321 > Email: [EMAIL PROTECTED] > Web: www.siriuscom.com > > ---------------------------------------------------------------------- > For LINUX-390 subscribe / signoff / archive access > instructions, send email to [EMAIL PROTECTED] with the > message: INFO LINUX-390 or visit > http://www.marist.edu/htbin/wlvindex?LINUX-390 > ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
