On Wed, 2007-08-29 at 16:38 -0400, Ross S. W. Walker wrote:
From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of israel.garcia@cimex.com.cu
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... does anybody knows how to setup a
software linux RAID on a proliant DL320 G4?
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When I setup my OS HD in a RAID1 I followed this recipe:
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- create 4GB LV called swap, formatted swap
OK. This particular item has aggravated me over many different posts and I've withstood the urge to holler "WHY"?
LVM adds another layer of (unnecessary) overhead. For swap to be usable, it must be formatted first, so it can't be expanded on-the-fly with LVM in use[1]. Further, expansion on-the-fly can be (effectively) accomplished by adding another partition or swap file (ugh! more unnecessary overhead) as needed when LVM is not in use.
Extra swap partitions/files can be easily enabled/disabled as desired on-the-fly without the extra overhead.
What's more, by having multiple swaps predefined and active at different priorities at boot-time, unexpected short-term surges in the use of swap can be gracefully accommodated. Since this requires no more space, has less overhead, is not dependent on anything other than primitive block device handling and seems to have as much flexibility and on-the-fly growth capability as one could want, I always asked "WHY?".
I am all ears (although it may not seem so) hoping to learn something new.
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[1] Although the mkswap man page discusses the formatting in minimal detail, it *appears* that a "tag" and bit-map of used blocks is needed/created when mkswap is run. If the vgextend command is used, after appropriate pvcreate functions, will the extension be properly formatted and used? Since you would not be adding a new swap partition/file, but extending an existing one, I suspect that the new space may go unused until a rerun of mkswap over the extended volume group is done, during which time the swap is not available at all. I don't know for sure and am too uninterested to research it that far when there seems no benefit from the use of LVM in the first place when all the potential benefits of LVM (only extensibility when in the context of swap) can be obtained other ways.
-- Bill