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RE: LVM on Linux

To: "'Ric Tibbetts'" <ric@xxxxxxxxxxxxxxxxxxxx>, Linux XFS Mailing List <linux-xfs@xxxxxxxxxxx>, JFS Discussion List <jfs-discussion@xxxxxxxxxxxxx>
Subject: RE: LVM on Linux
From: "Gonyou, Austin" <austin@xxxxxxxxxxxxxxx>
Date: Mon, 16 Jul 2001 15:46:57 -0500
Sender: owner-linux-xfs@xxxxxxxxxxx
It would be much nicer to know, what frame the 64-bit is that he's talking
about here. Also, If you have an enterprise storage system like EMC or
Hitatchi, you're probably running hardware level mirroring/RAID anyway. At
that point, there should be no need to worry if LVM is ready for that, since
you'r probably going to concatenate anyway or do striping. (since that's all
you need to do cause you're letting the hardware handle the other stuff for
you) So I don't see a big issue here when doing this. Plus, you could always
just use MD or RD anyway. For something like I use with EMC, and have
mirrored disks anyway, It's not a problem, cause I just stripe. Everything
else is already mirrored for me, so LVM is applying no major logic, other
than what it was built to do. Also, ELVM? I believe it's EVMS, from IBM. The
Enterprise Volume Management System. 

Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-796-9023
email: austin@xxxxxxxxxxxxxxx 

> -----Original Message-----
> From: Ric Tibbetts [mailto:ric@xxxxxxxxxxxxxxxxxxxx]
> Sent: Monday, July 16, 2001 3:09 PM
> To: Linux XFS Mailing List; JFS Discussion List
> Subject: LVM on Linux
> For anyone considering using LVM on Linux. You might want to take a 
> second to look at the following "short" article. It casts a 
> questionalble light on the current state of the LVM code.
> ================================================
> 0 Jun - 5 Jul (8 posts) Archive Link: [RFC][PATCH] first cut 
> 64 bit block
> support
>                   Summary by Zack Brown
> Ben LaHaise posted a patch and announced, "Below is the first 
> cut at making
> the block size limit configurable to 64 bits on x86, as well 
> as always 64
> bits on 64 bit machines. The audit isn't complete yet, but a 
> good chunk of
> it is done." [..] "The following should be 64 bit clean now: 
> nbd, loop,
> raid0, raid1, raid5." He gave links to two homepages at
> http://people.redhat.com/bcrl/lb/ and
> http://www.kvack.org/~blah/lb/. He added, "Ugly bits: I had 
> to add libgcc.a
> to satisfy the need for 64 bit division. Yeah, it sucks, but 
> RAID needs some
> more massaging before I can remove the 64 bit division 
> completely. This will
> be fixed." Chris Wedgwood proposed some changes to libgcc.a 
> to be less ugly,
> and Ben replied, "I'm getting rid of the need for libgcc 
> entirely. That's
> what "This will be fixed" means. If you want to expedite the 
> process, send a
> patch. Until then, this is Good Enough for testing purposes."
> Elsewhere, Ragnar Kjarstad was very happy about Ben's work, 
> asking if LVM
> was also 64-bit clean. Ben replied cryptically, "Errr, I'll 
> refrain from
> talking about LVM." Ragnar wanted some clarification, and Ben 
> explained:
> Fixing LVM is not on the radar of my priorities. The code is 
> sorely in need
> of a
> rewrite and violates several of the basic planning tenents 
> that any good
> code in the block layer should follow. Namely, it should have 
> 1) planned on
> supporting 64 bit offsets, 2) never used multiplication, 
> division or modulus
> on block numbers, and 3) don't allocate memory structures 
> that are indexed
> by block numbers. LVM failed on all three of these -- and 
> this si just what
> I noticed in a quick 5 minute glance through the code. Sorry, 
> but LVM is
> obsolete by design. It will continue to work on 32 bit block 
> devices, but if
> you try to use it beyond that, it will fail. That said, we'll 
> have to make
> sure these failures are graceful and occur prior to the user 
> having a chance
> at loosing any data.
> Now, thankfully there are alternatives like ELVM, which are working on
> getting the
> details right from the lessons learned. Given that, I think 
> we'll be in good
> shape
> during the 2.5 cycle.
> End Of Thread (tm).

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