[gentoo-user] Max Number of Partitions

[gentoo-user] Max Number of Partitions

[Mick]

Hi All,

I think that I have run out of partitions:

http://publib.boulder.ibm.com/infocenter/dsichelp/ds6000ic/index.jsp?topic=/com.ibm.storage.smric.help.doc/f2c_linuxscsilimit_2hsag9.html

Although I have created up to 17 partitions on a SATA, I cannot mount
them.  :-(

Before I start consolidating OS and data partitions to keep the number below
15, is there an alternative to this?
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Regards,
Mick

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Re: [gentoo-user] Max Number of Partitions

[Francesco Riosa]

Mick wrote:
> Hi All,
>
> I think that I have run out of partitions:
>
> http://publib.boulder.ibm.com/infocenter/dsichelp/ds6000ic/index.jsp?topic=/com.ibm.storage.smric.help.doc/f2c_linuxscsilimit_2hsag9.html
>
> Although I have created up to 17 partitions on a SATA, I cannot mount
> them.  :-(
>
> Before I start consolidating OS and data partitions to keep the number below
> 15, is there an alternative to this?
>   
Not that I know, sata disk are managed like scsi ones limiting the
number of partitions to 1-15 .

Someone, somewhere, one time told me that "lvm" could address that in
some manner but I've never seen how.


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Re: [gentoo-user] Max Number of Partitions

[Shawn Haggett]

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Hash: SHA1

Francesco Riosa wrote:
> Mick wrote:
>> Hi All,
>>
>> I think that I have run out of partitions:
>>
>> http://publib.boulder.ibm.com/infocenter/dsichelp/ds6000ic/index.jsp?topic=/com.ibm.storage.smric.help.doc/f2c_linuxscsilimit_2hsag9.html
>>
>> Although I have created up to 17 partitions on a SATA, I cannot mount
>> them.  :-(
>>
>> Before I start consolidating OS and data partitions to keep the number below
>> 15, is there an alternative to this?
>>   
> Not that I know, sata disk are managed like scsi ones limiting the
> number of partitions to 1-15 .
> 
> Someone, somewhere, one time told me that "lvm" could address that in
> some manner but I've never seen how. 

LVM would indeed be a solution. Instead of creating many disk
partitions, you would simply create one large one the size of the disk.
Then using LVM create as many virtual partitions as you need (I forget
the correct LVM terminology, I believe it's logical volumes). There are
many howto's out there on setting up LVM and explaining what it does, I
would suggest having a look at that.
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Re: [gentoo-user] Max Number of Partitions

[Alexander Skwar]

Francesco Riosa wrote:

> Someone, somewhere, one time told me that "lvm" could address that in
> some manner but I've never seen how.

Easy - with LVM, you (ideally) don't create any partitions. Instead,
you create so called "logical volumes" (LVs). On those LVs, you
the filesystems.

Alexander Skwar
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Re: [gentoo-user] Max Number of Partitions

[Alexander Skwar]

Shawn Haggett wrote:

> LVM would indeed be a solution. Instead of creating many disk
> partitions, you would simply create one large one the size of the disk.

Yes, you could. But if you go that way, you don't have to create
any partitions at all. Instead, you can also use "/dev/hda" with
LVM.

> Then using LVM create as many virtual partitions as you need (I forget
> the correct LVM terminology, I believe it's logical volumes). There are
> many howto's out there on setting up LVM and explaining what it does, I
> would suggest having a look at that.

Yep. But that means that the OP would have to backup and restore.

Alexander Skwar
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Re: [gentoo-user] Max Number of Partitions

[Jarry]

Alexander Skwar wrote:
> Shawn Haggett wrote:
>>LVM would indeed be a solution. Instead of creating many disk
>>partitions, you would simply create one large one the size of the disk.
> 
> Yes, you could. But if you go that way, you don't have to create
> any partitions at all. Instead, you can also use "/dev/hda" with LVM.

There are some limitations concerning lvm. I remember it is not
recommended to use it for <swap>, root and /boot (and probably
some more)...

Jarry
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Re: [gentoo-user] Max Number of Partitions

[Boyd Stephen Smith Jr.]

On Sunday 12 February 2006 06:45, Jarry <jarry@gmx.net> wrote about 'Re: 
[gentoo-user]  Max Number of Partitions':
> Alexander Skwar wrote:
> > Shawn Haggett wrote:
> >>LVM would indeed be a solution. Instead of creating many disk
> >>partitions, you would simply create one large one the size of the
> >> disk.
> >
> > Yes, you could. But if you go that way, you don't have to create
> > any partitions at all. Instead, you can also use "/dev/hda" with LVM.
>
> There are some limitations concerning lvm. I remember it is not
> recommended to use it for <swap>, root and /boot (and probably
> some more)...

Some distros (kubuntu, I believe) use LVM swap by default if you use LVM.  
While this could theoretically cause a problem, I'm fairly sure that any 
problem encountered would be an acceptable lvm2 or device-mapper bug.  
Putting swap on LVM does have the distinct advantage of allowing swap to 
be resized when you add or remove (!) ram -- I like swap to be ~2x ram.  I 
do not run LVM on swap, but that's because my swap is a resizable hw raid 
0 volume that I wouldn't want to store other data on.  (Data goes on raid 
5 or 6.)

It's not possible without some trickery to run /boot on LVM, since grub 
doesn't understand lvm and won't be able to find your files.  Lilo may 
make this possible, but I keep my /boot off of LVM because I prefer grub 
and it feels right to make boot a real partition.

Root on LVM is entirely possible.  I've run that way since I initially 
installed linux (well, initially, this time around).  You do have to 
create either an initrd or an initramfs that loads any needed modules that 
are not built in and activates the lvm logical volumes; genkernel can do 
this for you on gentoo.  Other distros also provide tools to do the same 
thing, I recommend placing root on LVM for the same reasons any mount 
point goes on LVM: dynamic growing and shrinking of the filesystem.  
Ext2/3, JFS, XFS, and ReiserFS all support growing a filesystem without 
unmounting it, I believe (I only use reiserfs).  [Shrinking a filesystem 
is another box of rocks, but I've done it successfully may a time.]

If you only have a single hard disk my recommended layout is:
/hda
  /hda1 -- /boot as big as you need it.  I use 1G, but that's overkill for 
most people.
  /hda2 -- extended partition container
  /hda5 -- space remaining after /boot and swap as a single LVM physical 
volume
  /hda6 -- swap; 2x RAM

You can than create a volume group with your single physical volume and 
begin cutting logical volumes out of it.  The default limit to the number 
of logical volumes in a volume group is 255.  When you need more storage 
you can add another hard drive, create a physical volume out of the whole 
drive (no need to partition), extend your volume group, and start growing 
your logical volumes across the new drive -- with no downtime if the drave 
can be hot plugged.

-- 
Boyd Stephen Smith Jr.
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ICQ: 514984 YM/AIM: DaTwinkDaddy
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Re: [gentoo-user] Max Number of Partitions

[Alexander Skwar]

Jarry wrote:
> Alexander Skwar wrote:
>> Shawn Haggett wrote:
>>>LVM would indeed be a solution. Instead of creating many disk
>>>partitions, you would simply create one large one the size of the disk.
>> 
>> Yes, you could. But if you go that way, you don't have to create
>> any partitions at all. Instead, you can also use "/dev/hda" with LVM.
> 
> There are some limitations concerning lvm. I remember it is not
> recommended to use it for <swap>,

Is that so? Why? Because of the risk of fragmentation?

> root and /boot

I agree. But with a cleverly crafted initrd (ramdisk),
/ can easily be put in a LVM.

> (and probably
> some more)...

No.

But all that is not a contradiction to what
I wrote :) Shawn wrote, that you could create
only *ONE* partition on the disk and use it for LVM.
I replied and said, that in this case, it might
make some sense to skip the partitioning alltogether
and use the complete disk (ie. without partitions)
for LVM.

Alexander Skwar
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Re: [gentoo-user] Max Number of Partitions

[Alexander Skwar]

Boyd Stephen Smith Jr. wrote:
> On Sunday 12 February 2006 06:45, Jarry <jarry@gmx.net> wrote about 'Re: 
> [gentoo-user]  Max Number of Partitions':
>> Alexander Skwar wrote:
>> > Shawn Haggett wrote:
>> >>LVM would indeed be a solution. Instead of creating many disk
>> >>partitions, you would simply create one large one the size of the
>> >> disk.
>> >
>> > Yes, you could. But if you go that way, you don't have to create
>> > any partitions at all. Instead, you can also use "/dev/hda" with LVM.
>>
>> There are some limitations concerning lvm. I remember it is not
>> recommended to use it for <swap>, root and /boot (and probably
>> some more)...
> 
> Some distros (kubuntu, I believe) use LVM swap by default if you use LVM.  
> While this could theoretically cause a problem,

Could it? How and why?

> I'm fairly sure that any 
> problem encountered would be an acceptable lvm2 or device-mapper bug.  

Ah, I see, that's what you mean. You're right.

> Putting swap on LVM does have the distinct advantage of allowing swap to 
> be resized when you add or remove (!) ram -- I like swap to be ~2x ram.

Well, it's very easy to create a swap file. As that's no longer
a disadvantage performancewise, what you stated is not an
argument for LVM.

Actually, because of the fragmentation, I'd understand if people
wouldn't want to resize the swap LV. Instead, I'd create another
swap LV.

> Root on LVM is entirely possible.  I've run that way since I initially 
> installed linux (well, initially, this time around).  You do have to 
> create either an initrd or an initramfs that loads any needed modules that 
> are not built in and activates the lvm logical volumes; genkernel can do 
> this for you on gentoo.

That's right. But if you also wish to use suspend-to-disk (swsusp
or http://suspend2.net/ ; suspend2-sources), you won't be able
to use a genkernel created initrd.

  Other distros also provide tools to do the same
> thing, I recommend placing root on LVM for the same reasons any mount 
> point goes on LVM: dynamic growing and shrinking of the filesystem.  
> Ext2/3, JFS, XFS, and ReiserFS all support growing a filesystem without 
> unmounting it, I believe (I only use reiserfs).  [Shrinking a filesystem 
> is another box of rocks, but I've done it successfully may a time.]
> 
> If you only have a single hard disk my recommended layout is:
> /hda
>   /hda1 -- /boot as big as you need it.  I use 1G, but that's overkill for 
> most people.

That's gross overkill :) I do very fine with only ~64 MB.

>   /hda2 -- extended partition container
>   /hda5 -- space remaining after /boot and swap as a single LVM physical 
> volume
>   /hda6 -- swap; 2x RAM

Very much like my layout :)

> You can than create a volume group with your single physical volume and 
> begin cutting logical volumes out of it.  The default limit to the number 
> of logical volumes in a volume group is 255.  When you need more storage 
> you can add another hard drive, create a physical volume out of the whole 
> drive (no need to partition), extend your volume group, and start growing 
> your logical volumes across the new drive

I'd *STRONGLY* urge to *NOT* do this, if we're talking about
normal consumer hard disks and especially if no backups are
done. What happens, if disk1 in a 2 disk VG goes broke?

Nah, too dangerous for me. I use multiple Volume Groups.

> -- with no downtime if the drave 
> can be hot plugged.

True.

Alexander Skwar
-- 
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church he sees fit, and to worship God in his own way, cannot be accused
of prejudice when we do not want to see public education connected with
religious control of the schools, which are paid for by taxpayers' money.
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Re: [gentoo-user] Max Number of Partitions

[Bo Andresen]

On Sunday 12 February 2006 16:12, Boyd Stephen Smith Jr. wrote:
>   /hda1 -- /boot as big as you need it.  I use 1G, but that's overkill for
> most people.

Can't help being curious - how much of that space do you actually use??
I currently use 48 MB on /boot.

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Re: [gentoo-user] Max Number of Partitions

[Boyd Stephen Smith Jr.]

On Sunday 12 February 2006 13:38, Alexander Skwar 
<listen@alexander.skwar.name> wrote about 'Re: [gentoo-user]  Max Number 
of Partitions':
> Boyd Stephen Smith Jr. wrote:
> > On Sunday 12 February 2006 06:45, Jarry <jarry@gmx.net> wrote about
> > 'Re:
> >
> > [gentoo-user]  Max Number of Partitions':
> >> There are some limitations concerning lvm. I remember it is not
> >> recommended to use it for <swap>, root and /boot (and probably
> >> some more)...
> >
> > Some distros (kubuntu, I believe) use LVM swap by default if you use
> > LVM. While this could theoretically cause a problem,
>
> Could it? How and why?

I'm thinking of some obsure case where the code or data needed to read swap 
has been swapped out.

> > Putting swap on LVM does have the distinct advantage of allowing swap
> > to be resized when you add or remove (!) ram -- I like swap to be ~2x
> > ram.
>
> Well, it's very easy to create a swap file. As that's no longer
> a disadvantage performancewise, what you stated is not an
> argument for LVM.

I don't like swap files cluttering up my filesystem. :)

> > Root on LVM is entirely possible.  I've run that way since I initially
> > installed linux (well, initially, this time around).  You do have to
> > create either an initrd or an initramfs that loads any needed modules
> > that are not built in and activates the lvm logical volumes; genkernel
> > can do this for you on gentoo.
>
> That's right. But if you also wish to use suspend-to-disk (swsusp
> or http://suspend2.net/ ; suspend2-sources), you won't be able
> to use a genkernel created initrd.

I roll my own initrd / initramfs anyway, it's not really that hard just a 
bit tedious.

> >   /hda1 -- /boot as big as you need it.  I use 1G, but that's overkill
> > for most people.
>
> That's gross overkill :) I do very fine with only ~64 MB.

I have 4G of RAM.  I have an rescue initrd on boot that contains a gentoo 
install with all my recovery tools, basically a livecd.  /boot is not 
full, but 1G is a nice round number.

> > You can than create a volume group with your single physical volume
> > and begin cutting logical volumes out of it.  The default limit to the
> > number of logical volumes in a volume group is 255.  When you need
> > more storage you can add another hard drive, create a physical volume
> > out of the whole drive (no need to partition), extend your volume
> > group, and start growing your logical volumes across the new drive
>
> I'd *STRONGLY* urge to *NOT* do this, if we're talking about
> normal consumer hard disks and especially if no backups are
> done. What happens, if disk1 in a 2 disk VG goes broke?

Um, activate the vg in partial mode and lvols on the good disk will still 
be accessible -- I think even writable, but I could be wrong on that 
point.  I'm not sure if that's in the standard lvm startup scripts on 
gentoo, but my initrd includes vgscan -P; vgchange -Pay.

> Nah, too dangerous for me. I use multiple Volume Groups.

Then you can't have a lv that's bigger than a single pv or migrate data 
between pvs (to switch them out or w/e) using pvmove.

You are seriously crippling the usefulness of lvm if you always use a 1 pv 
= 1 vg rule.

-- 
Boyd Stephen Smith Jr.
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ICQ: 514984 YM/AIM: DaTwinkDaddy
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Re: [gentoo-user] Max Number of Partitions

[Richard Fish]

On 2/12/06, Boyd Stephen Smith Jr. <bss03@volumehost.com> wrote:
> I'm thinking of some obsure case where the code or data needed to read swap
> has been swapped out.

BTW, I have been using swap on LVM (on an encrypted PV) for quite some
time, without any trouble, including using suspend-to-ram and
suspend-to-disk.  If there were an obscure case, I think that would be
it.

I am pretty sure the kernel locks the device-mapper code into memory,
so that it can never be swapped out.

-Richard

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RE: [gentoo-user] Max Number of Partitions

[Michael Kintzios]

> -----Original Message-----
> From: Boyd Stephen Smith Jr. [mailto:bss03@volumehost.com] 
> Sent: 13 February 2006 01:32
> To: gentoo-user@lists.gentoo.org
> Subject: Re: [gentoo-user] Max Number of Partitions
> 
> 
> Um, activate the vg in partial mode and lvols on the good 
> disk will still 
> be accessible -- I think even writable, but I could be wrong on that 
> point.  I'm not sure if that's in the standard lvm startup scripts on 
> gentoo, but my initrd includes vgscan -P; vgchange -Pay.
> 
> > Nah, too dangerous for me. I use multiple Volume Groups.
> 
> Then you can't have a lv that's bigger than a single pv or 
> migrate data 
> between pvs (to switch them out or w/e) using pvmove.
> 
> You are seriously crippling the usefulness of lvm if you 
> always use a 1 pv 
> = 1 vg rule.

Thank you all for the responses!  It's taken me sometime to check my
mail and they've piled up.  :)

Two quick Q's:

Current partitions 1, 13, 14, 15 and 16 are NTFS.  As I understand it
LVM is a software solution that works happily with Linux.  What happens
when my other half tries to boot into WinXP?  Are we going to have a
major domestic because I hosed *her* computer?

I believe Alexander mentioned it, but the reason I have placed
directories like /usr/portage into different partitions is to minimise
data fragmentation.  How does this work in an LVM set up?
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Mick

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Re: [gentoo-user] Max Number of Partitions

[Alexander Skwar]

Michael Kintzios wrote:

> Two quick Q's:
> 
> Current partitions 1, 13, 14, 15 and 16 are NTFS.  As I understand it
> LVM is a software solution that works happily with Linux.

Yes. And only Linux - meaning, that if you'd boot
FreeBSD or Solaris, you won't be able to use your
filesystems.

>  What happens
> when my other half tries to boot into WinXP?

She won't be able to access the Linux filesystems.

>  Are we going to have a
> major domestic because I hosed *her* computer?

No. Windows will only see one partition - the partition
holding the "physical volume" (PV) which contains your
volume group  (VG) which, in turn, contains the logical
volumes (LV) on which you'll, finally *G*, have your
filesystems.

> I believe Alexander mentioned it, but the reason I have placed
> directories like /usr/portage into different partitions is to minimise
> data fragmentation.

I'm talking about a different kind of fragmentation. With
LVM, logical volumes ("partitions") don't have to be consecutive.
Indeed, most of the time they won't be. So, suppose you
create lvol1 and lvol2. Now you wish to extend lvol1. What
will happen is, that the phsyical extents ("blocks") for
lvol1 are "in front of" and "behind" lvol2 (simply put).

>  How does this work in an LVM set up?

Filesystems don't "see" that they are on logical
volumes. This means, that the filesystem fragmentation
will happen just as as it normally does.

Alexander Skwar
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[gentoo-user] Re: Max Number of Partitions

[Mick]

Alexander Skwar wrote:

> Michael Kintzios wrote:
> 

>>  How does this work in an LVM set up?
> 
> Filesystems don't "see" that they are on logical
> volumes. This means, that the filesystem fragmentation
> will happen just as as it normally does.

If I read you right, then /usr will behave the same with regards to data
fragmentation (in the non-LVM sense of the word) whether in a primary
partition on its own, or in a LV also on its own?
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Re: [gentoo-user] Max Number of Partitions

[Boyd Stephen Smith Jr.]

On Monday 13 February 2006 08:54, "Michael Kintzios" 
<michaelkintzios@lycos.co.uk> wrote about 'RE: [gentoo-user]  Max Number 
of Partitions':
> Current partitions 1, 13, 14, 15 and 16 are NTFS.  As I understand it
> LVM is a software solution that works happily with Linux.  What happens
> when my other half tries to boot into WinXP?  Are we going to have a
> major domestic because I hosed *her* computer?

Windows will not be able to see LVs; These will have to remain as 
partitions or you can use the windows equivalent of LVM.  It's something 
like dynamic disk management or dynamic volume manager... I don't use 
windows much.

> I believe Alexander mentioned it, but the reason I have placed
> directories like /usr/portage into different partitions is to minimise
> data fragmentation.  How does this work in an LVM set up?

The filesystem will see a LV the same way it sees a partition, as a single 
contiguous block device.  Filesystem level fragmentation will happen as 
normal on this block device.

However, LVM does introduce the possibility for the LV itself to become 
fragmented.  You can prevent this by marking the LV(s) as contiguous, but 
that will prevent you from extending the LV in some cases.  Generally LV 
fragmentation is much less of a problem because LVs change size less often 
than the files on the filesystems they host change size.

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Re: [gentoo-user] Re: Max Number of Partitions

[Alexander Skwar]

Mick wrote:

> If I read you right, then /usr will behave the same with regards to data
> fragmentation (in the non-LVM sense of the word) whether in a primary
> partition on its own, or in a LV also on its own?

Yes, exactly.

Alexander Skwar
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