kernel recognizing large (> 2.1 TB) block devices ?

[Randall A. Jones]

Les Mikesell wrote:

>On Thu, 2005-01-13 at 12:08, Randall A. Jones wrote:
>  
>
>>This SCSI card is an Adaptec 39160.
>>The RAID is a Nexsan ATABoy2 with a SCSI interface.
>>It seems that the driver recognizes the need and is trying to use the 
>>READ(16) command but that it is failing.
>>from log:
>>
>>sdc : very big device. try to use READ CAPACITY(16).
>>sdc : READ CAPACITY(16) failed.
>>    
>>
>
>Can you configure smaller logical partitions on the device and combine
>them with LVM? 
>
>  
>
This is a good question.  In theory, I think the answer is yes, but I'm 
not sure about potential limitations of LVM regarding maxium number of 
blocks in a volume group or logical volume.  I've seen messages like the 
following in the past (FC2 install).
[root at aes init.d]# vgcreate -s 128 aesvg0 /dev/sdc
vgcreate -- INFO: maximum logical volume size is 2 Terabyte
vgcreate -- doing automatic backup of volume group "aesvg0"
vgcreate -- volume group "aesvg0" successfully created and activated

for LVM2, vgcreate states a maximum logical volume of 2TB.
I have not found or read satisfactory documentation yet to answer 
questions about
size limitations of creating a > 2TB VG or LVM.
Is anyone familiar with LVM enough to say that it will support large 
resulting volumes?  What is the maxium size LV possible in LVM2, kernel 
2.6 ?
Where is a good place to read details about the capabilities?
I have found HowTo documents to be generalized for a common case of a 
few "normal" sized devices joined in an LV with no information about 
what to do if you want a large LV.
The vgcreate man page says that you can create a PE (physical extent) up 
to 16GB in size and that there is a maxium of 64k PEs per LV.  16GB*64K 
= ~1.125 PB (PetaBytes).  Is that right?
That begs the question why vgcreate talks about a 2TB limit.  Legacy 
message?  from a time before LBD in the kernel?

Perhaps I need to learn more about LVM before I make up my mind on its 
capabilities.
Any helpful hints or guidance would be much appreciated.

Randall

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Randall Jones     GST      NASA Goddard Space Flight Center
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