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Re: [linux-lvm] LVM limit on PE's/size?



Scott,

with your PE size of 32MB, you can achieve to create LVs up to 2TB in size
(actually it is a little bit less than 2TB, because every LV can have up
to 64K - 2 extents). You can have multiple 2TB LVs this way, because your
VG capacity is in no means limited to 2TB! In theory you could have 128 SCSI
IDs with 8 LUNs each providing up to 1 or 2TB in 1 VG.

Because your PVs are smaller than 1TB in size, you will not suffer from
the block adrdessing sign bit danger Andreas was explaining in his email.

In general you should plan for the largest possible Logical Volume size
during the lifetime of a Volume Group and set the Physical Extent size
(vgcreate -s) acordingly. Even though Linux does not support more than 2TB
per block device today, it will be in the future and you won't suffer from
the LVM1 constraint ITR.

Regards,
Heinz    -- The LVM Guy --


On Tue, Nov 27, 2001 at 02:00:07PM -0600, Scott P wrote:
> Andreas,
> 
> Thanks so much for the insight!
> 
> Here is some ouput, it looks like we might be ok?
> Please comment, if possible, thanks...
> 
> -Scott
> 
> [root ptb3 pichelma]# /sbin/pvdisplay /dev/sdb1
> --- Physical volume ---
> PV Name               /dev/sdb1
> VG Name               exp300_2
> PV Size               440.71 GB / NOT usable 26.75 MB [LVM: 176 KB]
> PV#                   2
> PV Status             available
> Allocatable           yes (but full)
> Cur LV                1
> PE Size (KByte)       32768
> Total PE              14102
> Free PE               0
> Allocated PE          14102
> PV UUID               1gKwp2-dotn-0WJU-5FwZ-uScI-OyMH-SHVw5F
> 
> 
> [root ptb3 pichelma]# /sbin/pvdisplay /dev/sdc1
> --- Physical volume ---
> PV Name               /dev/sdc1
> VG Name               exp300_2
> PV Size               440.71 GB / NOT usable 26.75 MB [LVM: 176 KB]
> PV#                   1
> PV Status             available
> Allocatable           yes (but full)
> Cur LV                1
> PE Size (KByte)       32768
> Total PE              14102
> Free PE               0
> Allocated PE          14102
> PV UUID               ciUWIf-i9OO-okne-Fs6R-fjU1-NPpr-Ml4p8L
> 
> 
> [root ptb3 pichelma]# /sbin/pvdata -P /dev/sdb1
> --- Physical volume ---
> PV Name               /dev/sdb1
> VG Name               exp300_2
> PV Size               440.71 GB / NOT usable 26.75 MB [LVM: 176 KB]
> PV#                   2
> PV Status             available
> Allocatable           yes (but full)
> Cur LV                1
> PE Size (KByte)       32768
> Total PE              14102
> Free PE               0
> Allocated PE          14102
> PV UUID               1gKwp2-dotn-0WJU-5FwZ-uScI-OyMH-SHVw5F
> 
> 
> [root ptb3 pichelma]# /sbin/pvdata -P /dev/sdc1
> --- Physical volume ---
> PV Name               /dev/sdc1
> VG Name               exp300_2
> PV Size               440.71 GB / NOT usable 26.75 MB [LVM: 176 KB]
> PV#                   1
> PV Status             available
> Allocatable           yes (but full)
> Cur LV                1
> PE Size (KByte)       32768
> Total PE              14102
> Free PE               0
> Allocated PE          14102
> PV UUID               ciUWIf-i9OO-okne-Fs6R-fjU1-NPpr-Ml4p8L
> 
> 
> 
> Andreas Dilger wrote:
> 
> > On Nov 27, 2001  11:34 -0600, Scott P wrote:
> > > We are planning to add a 3 rd EXP300 array to out current server w/ 2
> > > EXP300's in place already!  We WILL surpass the 1 TB size, if possible?
> >
> > Depends if the driver does 32-bit block numbers with signed or unsigned
> > values.  The absolute maximum supported by 2.4 kernels is 2TB devices.
> > I don't know if 2.2 will support > 1TB devices, but it is possible.
> >
> > > Linux ptb3 2.2.19 #2 SMP Tue Jul 24 11:53:29 CDT 2001 i686 unknown
> > >
> > > We are using:
> > > lvm_0.9.1_beta7
> > > reiserfsprogs-3.x.0j
> >
> > Get newer LVM tools, like 1.0.1, because the old ones have lots more bugs.
> > Beta 7 has the PE alignment bug, so you should upgrade the tools even if
> > you can't upgrade the kernel.
> >
> > > Here is the current filesystem and size:
> > >
> > > /dev/exp300_2/exp300_lv2 924160464 891307744  32852720      97% /files1
> >
> > > Q: Why are my logical volumes limited to 256 GB in size?
> > > A: This is NO absolute limit but it depends on the physical extent size
> > > you configured at volume group creation time.
> >
> > Check what "pvdata -P /dev/whatever" tells you about the PE size.  If
> > it is 16386kB, then you are limited to 1TB in size.  If it is larger
> > than that, you _may_ be able to go past 1TB, but you may not, depending
> > on whether your drivers and kernel work properly or not.
> >
> > Cheers, Andreas
> > --
> > Andreas Dilger
> > http://sourceforge.net/projects/ext2resize/
> > http://www-mddsp.enel.ucalgary.ca/People/adilger/
> >
> > _______________________________________________
> > linux-lvm mailing list
> > linux-lvm sistina com
> > http://lists.sistina.com/mailman/listinfo/linux-lvm
> > read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
> 
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm sistina com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

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