Is what Bill Jones is saying correct?
I am just starting on XFS, and dont
have enough familiarity with it's
architecture.
Cheers,
Joe
>-----Original Message-----
>From: William L. Jones [mailto:jones@xxxxxxxxxxxxxxxxxx]
>Sent: Friday, September 01, 2000 11:02 AM
>To: Steve Lord; William L. Jones
>Cc: cattelan@xxxxxxxxxxx; Davida, Joe; 'linux-xfs@xxxxxxxxxxx'
>Subject: Re: 2 Terabyte File System Size Limitation
>
>
>At 11:44 AM 9/1/00 -0500, Steve Lord wrote:
>
>> > >
>> > >XFS has additional problems with inode numbers overflowing the
>> > >standard 32bit container once the file system its self
>goes over 2TB.
>> >
>> > I was wondering about that. It seem like you should be
>able to control
>> > this with mkfs.xfs by setting agcont and setting the
>> > agsize instead of letting mkfs.xfs set them. I don't
>think that many
>> people
>> > need a file system that can contain a billion files. Just a few
>> > hundred million will due. The only down side in doing this
>> > is that the inode info may not be splattered across all of
>the file system
>> > like it would if you used the mkfs.xfs defaults.
>> >
>> >
>>
>>
>>The problem is not the number of inodes the system will allow
>you to create,
>>it is where they are created. An XFS inode number is actually
>a disk address,
>>once the filesystem goes beyond the 2Tbyte limit inodes can
>have addresses
>>which are beyond this boundary and hence over flow the 32 bit
>inode field.
>>
>>At the moment there is no way of restricting inodes to
>specific allocation
>>groups, but I suppose it would be possible to do this. In
>fact it might be
>>a simpler solution than anything else. The consequences are :
>>
>>1. moving an existing filesystem from Irix will still
>potentially leave
>> us with inodes beyond the boundary.
>>
>>2. it will change the distribution of inodes in the
>filesystem, which will
>> in turn change how data is distributed. There is a danger
>that the first
>> 2 Tbytes would have to become fairly full and hence
>potentially fragmented
>> before much data made it into the rest of the filesystem.
>This will take
>> some thinking about.
>>
>>Steve
>>
>>
>
>
>It really is very simple. XFS just the inode shifted down
>by the by the log2(number of inodes per disk block)+log(agsize) to find
>the ag group that the inode is in.
>
>The the maxima inode is just:
>
> agcount<<log2(number of inodes per disk block)+log(agsize
>in blocks)
>
>Inodes on xfs are restricted to a specific allocation group. Each
>allocation group can only contain agsize/(inodes per disk
>block) inodes.
>
>For any xfs file system with mkfs.xfs we can choose agcount
>and agsize to
>insure that that the maxium inode less then 32 bits for any
>size of an xfs
>file system.
>
>Like I said the only draw back is that the inode regions will not cover
>be spread over all the disk systems which is what mkfs.xfs does by its
>chose of agcount and agsize.
>
>It looks like you should be able to make 16TB xfs file system with lVM,
>if LVM really allows you to address 16TB of disk in a partation,
>on linux so long as you don't use the mkfs.xfs defaults.
>
>I could live with that.
>
>Bill Jones
>
>
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