[Leaplist] "SWAP" --- " RHEL Logical Volume Management System"

Sat May 10 22:04:19 EDT 2008

John Simpson---Thank you, John.
Your message sent me, a beginner, to Google a number of times.
I had to look up IDE, ATA, SATA and other concepts.
The LVM system for partitioning IDE or SATA disks strikes me as 
un-necessary
for a User unlikely to ever need such sophisticated application.

Google really is one's friend.
And so are all the good men who have chimed in to help my understanding.

Many thanks,

William
Flagler Beach

John Simpson wrote:
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> On 2008-05-05, at 1822, William H. Ferguson wrote:
>>
>> I was previously somewhat familiar with the 4th Partition in Linux 
>> which is called the Extended Partition. I understood that many 
>> Directories could be created in that Extended 4th Partition
>
> the idea of an "extended partition" has nothing to do with linux per 
> se; it's been around since IBM first built a PC with a hard drive in it.
>
> under the IBM partition table format (which is used by MS-DOS, 
> windows, linux, and many other operating systems) the partition table 
> physically has room for four partitions. if somebody needs more than 
> four, they can make one of the four into an "extended partition", 
> which itself contains a four-slot partition table, which makes it 
> possible to have up to seven usable partitions on a disk.
>
> there is functionally no difference between a partition within the 
> first partition table (which would be called /dev/hda[0-3]) and a 
> partition within the extended partition's partition table (which would 
> be called /dev/hda[4-7].)
>
> the "extended partition" doesn't contain directories, it contains 
> partitions. each partition, whether 0-3 or 4-7, contains a 
> filesystem... and the filesystem contains directories.
>
>
>> I used that Partitioning approach back around Fedora Core 5 to 
>> install Fedora. I created /boot/ / root and Swap as Primary 
>> Partitions and then created the Extended Partition as my 4th Primary 
>> Partition. Within that 4th Partition I created several Partitions 
>> which I wanted, and one of them was /home.
>>
>> With that prologue I write to ask these two basic (to me) questions:
>>
>> 1. Can the User still install a Linux Distribution (I happen to use 
>> Fedora Core 8 now) without ever using the Logical Volume Management 
>> System if he so desires? Similar to what I summarized in two 
>> paragraphs above this one.
>
> yes. however, you have to do a "custom" layout, because fedora's 
> default (if you let it do whatever it wants with your disk) is to 
> install LVM and create all of its filesystems as LVM containers.
>
> unfortunately, it takes all available space when it does this, so even 
> if you want to use LVM but leave some open room for future partitions, 
> you have to do a "custom" layout, and create the PV (or PVs), VG, and 
> LVs by hand.
>
> i concentrated on LVM for your system, because it was already running 
> with LVM. you didn't want to re-install from scratch, so what we 
> needed to do was shrink your "/" filesystem (which was almost the 
> entire disk) and the LVM container which holds it, and that would have 
> freed up enough space for you to create additional LVM containers to 
> set up separate partitions for each family member's home directory.
>
>
>> 2. Does SWAP always have to be a Primary Partition?
>> Or can SWAP be a not-Primary Partition?
>
> first, please put the distinction between "primary" and "non-primary" 
> partitions out of your mind. THERE IS NO DIFFERENCE. they are both 
> "physical parititions", in that they represent a physically contiguous 
> series of blocks on the disk.
>
> swap space, like any other filesystem, can be created on ANY 
> partition, whether it's in a primary partition, an extended partition, 
> an LVM logical volume, a RAID container, or a raw disk without a 
> partition table at all (if you structure it correctly.) all that 
> matters is that the kernel is able to address it as a block device. 
> for that matter, you can even create a file and use that as swap 
> space, although it's not as fast as devoting a partition to it.
>
> the ONLY restriction on what can be on which kind of partition, is the 
> filesystem containing the kernel and initrd files. it must be on a 
> physical partition (primary or non-primary, it doesn't matter) instead 
> of an LVM or RAID-5 container.
>
> in addition, on systems which boot from IDE drives, the filesystem 
> containing the kernel and initrd files MUST be contained totally 
> within the first 1024 cylinders of the disk, so that the BIOS disk 
> services (which on most machines can't address cylinder numbers higher 
> than 1023) can be used to load the kernel and initrd into memory in 
> the first place. where your machine has a SATA drive, which linux sees 
> as SCSI, the 1024-cylinder restriction doesn't apply to you.
>
> all that matters for you is that IF you choose to use LVM, your 
> "/boot" directory must be on a physical partition- it cannot be within 
> an LVM container.
>
>
>> If User is using the Logical Volume Management Partitioning program 
>> for installation of Partitions, can User put SWAP in the Logical 
>> Volume Management Group as a Logical Volume rather than make it a 
>> Primary Partition?
>
> yes.
>
>
>> I don't remember where I got the idea that Swap had to be a Primary 
>> Partition but I have had that notion in my head for a few years. 
>> John, during Install-Fest, said that SWAP could be either a Primary 
>> Partition, or a non-Primary Partition or could be a Partition under 
>> the Logical Volume Management System.
>
> correct. swap space can be anywhere, as long as the kernel is able to 
> address it in a random-access fashion, as it can with a block device, 
> or a file. if you're really a masochist, you can even use a USB stick 
> as swap space... or set up a ramdisk and use that as swap space, but 
> that kinda defeats the point of using swap in the first place...
>
>
> - --------------------------------------------------------
> | John M. Simpson -- KG4ZOW -- Programmer At Large |
> | http://www.jms1.net/ <jms1 at jms1.net> |
> - --------------------------------------------------------
> | Hope for America -- http://www.ronpaul2008.com/ |
> - --------------------------------------------------------
>
>
>
>
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