[linux-lvm] any way to locate vg's on, say, /etc?

[linux-lvm] any way to locate vg's on, say, /etc?

[Steven Lembark]

currently have a choice:  LVM or devfs.  since devfs essentially
wipes out any /dev/blah dir's created after boot when it is 
remounted using /dev/ w/ vgcreate causes pain.  short of hacking
soft links or archiving the devices w/ cpio every boot, putting
the vol group dir's outside dev seems like the easiest fix.

personal guess would be /etc or /LVM as likely places.

just wondering if "/dev" is hard-coded or configurable
in the kernel headers somewhere...

-- 
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 lembark@wrkhors.com                                   800-762-1582

Re: [linux-lvm] any way to locate vg's on, say, /etc?

[Russell Coker]

On Sunday 07 January 2001 10:54, Steven Lembark wrote:
> currently have a choice:  LVM or devfs.  since devfs essentially
> wipes out any /dev/blah dir's created after boot when it is
> remounted using /dev/ w/ vgcreate causes pain.  short of hacking
> soft links or archiving the devices w/ cpio every boot, putting
> the vol group dir's outside dev seems like the easiest fix.
>
> personal guess would be /etc or /LVM as likely places.
>
> just wondering if "/dev" is hard-coded or configurable
> in the kernel headers somewhere...

You can mount devfs on another location...

But that's not the solution either.  Every kernel driver should have
#ifdef CONFIG_DEVFS_FS
and then some code to create device nodes at the time it registers it's use 
of the device numbers.
Device drivers that aren't devfs aware are buggy.
/etc is totally wrong, it's only supposed to have config files.  Doing 
otherwise would make Linux as crappy as Solaris.

The best solution to these types of problems would be to make devfs mandatory 
for LVM and then only use the devfs functionality.  Then device numbers stop 
being a problem.

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Re: [linux-lvm] any way to locate vg's on, say, /etc?

[Joe Thornber]

> currently have a choice:  LVM or devfs.  since devfs essentially

LVM 0.9 supports devfs.

- Joe

Re: [linux-lvm] any way to locate vg's on, say, /etc?

[Russell Coker]

On Tuesday 09 January 2001 17:28, you wrote:
> > Why is it impossible for make LVM configuration something that gets
> > started automatically at boot when it's possible to make RAID start at
> > boot?
>
> see above:  if you store enough data to vgimport the
> volumes at boot time (however it is done) then you
> don't need to store the volume group inodes in any
> persistent storage.
>
> catch is that storing all of the data used to recover the
> media on the media to be recovered makes recovery more
> difficult when the media fries [not if].

For serious systems hard disk failure modes should be considered as discrete 
events.  A hard drive is either working perfectly (all data written is read 
back correctly) or it is failed (it has returned an error so we put it 
offline and replace it with a hot spare or send an emergency alert to the 
administrator).
All data should be mirrored.  Hard drives are cheap.  I recently bought 
myself two 46G hard drives for less than I once paid for a single 70M drive, 
and less than I later paid for a 330M drive.
My "gut feeling" is that drives are more susceptible to damage now.  I know 
of cases of older 3600rpm drives being dropped, being hit by a car while 
operating (car entered building through the wall of the computer room), and 
suffering numerous other mechanically damaging events without data loss.  I 
belive that modern 10K rpm drives are not as solid.
Also drives are more susceptible to heat problems.  3600rpm drives could 
operate with all their air-holes blocked and while surrounded by other hard 
drives without problems.  You can't stack two new 10K rpm drives without good 
fans.

If things are correctly setup then you can lose a single drive at any time 
without data loss.  If LVM on-disk data structures can be recovered with a 
drive dead (which is the case if LVM is running on top of RAID 1) then there 
shouldn't be a problem.

IMHO if you run LVM across multiple disks without RAID-1 backing then you 
probably don't care much for your data.  Probability of no-failure of the 
system is obtained by multiplying the probability of no-failure of each part.

So if during a time period there is a 10% chance that a hard drive will fail 
then the probability of no-failure is 0.9.  Therefore the probability of two 
drives in an LVM set not failing is 0.81 over the same time period.

> > One thing that I plan to do is create LVM, devfs, and RAID rescue disks
> > for Debian.  So far I have not had time.  :(
>
> if your software RAID gets blown you're in pretty deep
> water.  HP's trick of forcing the boot, primbary swap

RAID rescue disks does not inherantly mean rescue from RAID problems.  It 
also means that if (for example) you have a non-autodetect RAID setup and you 
want to fix config files on that file system that prevent booting (eg a 
corrupted /etc/fstab) then you can do it.  Also you need RAID enabled rescue 
disks to install onto RAID in the first place, or to make a non-RAID root 
file partition into a RAID partition.

> and root voumes to be on contiguous storage from cyl0
> makes recovering LVM a snap:  just boot without it,

If I did that then I'd only have one other file system left on most of my 
machines and thus would not be able to achieve much benefit from LVM!

> q:  what is there to recover from a damaged devfs?  i
> though the entire file system was virtual (a la /proc).

Correct, Devfs can't get damaged in any way that a reboot won't fix
(rm -rf /dev/* will be hard to fix without a reboot).

But if you use devfs for /etc/fstab, /etc/lilo.conf, etc then using rescue 
disks that don't support devfs will be painful for you.  Also once you start 
using devfs everywhere you get used to the device names and don't want to 
stop using them (having to remember two names for everything is painful).

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[linux-lvm] hard drive shock tolerance

[zoo1]

On Wed, Jan 10, 2001 at 01:39:13AM +1100, Russell Coker wrote:

[...]
>My "gut feeling" is that drives are more susceptible to damage now.  I know 
>of cases of older 3600rpm drives being dropped, being hit by a car while 
>operating (car entered building through the wall of the computer room), and 
>suffering numerous other mechanically damaging events without data loss.  I 
>belive that modern 10K rpm drives are not as solid.

speaking as someone who has personally dropped (and destroyed) 36GB 10K
rpm SSA disk drives, i can attest that modern-day disks are sensitive.
those disks i mentioned fell about 20-30cm onto concrete, and were
toast.

(in all fairness, other identical drives that fell right with them
survived, so that shock must have been just on the boundary. i ended up
avoiding the blame, due to the unreasonable and careless way the disks
had been packaged and shipped - which was lucky for me, genuine IBM
disks of this type cost around $1600 USD apiece...)

hit by a car? you're serious? i can't even imagine a modern disk
surviving that! i've seen 9GB SCSI disks destroyed by an approximately
60cm drop onto wooden benchtop, covered with a (thin) antistatic rubber
mat; that wasn't me dropping those, though - about $800 apiece, IIRC...

>Also drives are more susceptible to heat problems.  3600rpm drives
>could operate with all their air-holes blocked and while surrounded by
>other hard drives without problems.  You can't stack two new 10K rpm
>drives without good fans.

i'll take your word for it. myself, i never see drives like that in
PCs, just in workstations and RAID arrays with more than adequate
cooling; but then again, i don't see PCs much these days anymore.

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Re: [linux-lvm] hard drive shock tolerance

[Russell Coker]

On Thursday 11 January 2001 11:54, zoo1@corecomm.net wrote:
> On Wed, Jan 10, 2001 at 01:39:13AM +1100, Russell Coker wrote:
> >My "gut feeling" is that drives are more susceptible to damage now.  I
> > know of cases of older 3600rpm drives being dropped, being hit by a car
> > while operating (car entered building through the wall of the computer
> > room), and suffering numerous other mechanically damaging events without
> > data loss.  I belive that modern 10K rpm drives are not as solid.
>
> hit by a car? you're serious? i can't even imagine a modern disk

An idiot in the drive of the next house mistook the accelerator pedal in an 
automatic car for the brake, she kept pressing it harder when the car didn't 
stop.
The car entered through a solid brick wall that the computer had been in 
front of.  The computer ended up on the floor at the far side of the room (~4 
meters away).
The car was stopped from going further through the house by rubble which 
supported much of the weight of the car and prevented the rear wheels from 
gaining traction.  For some time the car was burning rubber on the spot...

> >Also drives are more susceptible to heat problems.  3600rpm drives
> >could operate with all their air-holes blocked and while surrounded by
> >other hard drives without problems.  You can't stack two new 10K rpm
> >drives without good fans.
>
> i'll take your word for it. myself, i never see drives like that in
> PCs, just in workstations and RAID arrays with more than adequate
> cooling; but then again, i don't see PCs much these days anymore.

Most hardware work I do is with PCs.  When dealing with rack mounted server 
equipment I generally do the software and someone else deals with the 
hardware.
Given a choice I prefer hard drives with lower rotational speeds because of 
the lesser heat production.  Read the spec sheets and you'll see that as a 
general rule 10K rpm drives use twice as much power as 7200 rpm drives, twice 
the power == twice the heat!

The really worrying thing about heat death is that it's one of the few ways 
that I could imagine two hard drives in a mirrored set dieing before I get a 
chance to replace one!

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Re: [linux-lvm] hard drive shock tolerance

[Scott Laird]

On Sat, 13 Jan 2001, Russell Coker wrote:
> Given a choice I prefer hard drives with lower rotational speeds because of 
> the lesser heat production.  Read the spec sheets and you'll see that as a 
> general rule 10K rpm drives use twice as much power as 7200 rpm drives, twice 
> the power == twice the heat!

Hmm.  Seagate's current 9GB 7200 RPM drive, the ST39236LC draws 7W when
idle.  Their current 9 GB 10k RPM drive, the ST39204LC draws 8.5W when
idle.  IMHO, that's not really very significant anymore, especially when
your CPU eats 20-70W.  Both of these numbers are way better then drives
only a generation or two back -- last year's ST39175 (9 GB, 7200 RPM) drew
9.75W when idle.


Scott

Re: [linux-lvm] hard drive shock tolerance

[Russell Coker]

On Saturday 13 January 2001 08:41, Scott Laird wrote:
> On Sat, 13 Jan 2001, Russell Coker wrote:
> > Given a choice I prefer hard drives with lower rotational speeds because
> > of the lesser heat production.  Read the spec sheets and you'll see that
> > as a general rule 10K rpm drives use twice as much power as 7200 rpm
> > drives, twice the power == twice the heat!
>
> Hmm.  Seagate's current 9GB 7200 RPM drive, the ST39236LC draws 7W when
> idle.  Their current 9 GB 10k RPM drive, the ST39204LC draws 8.5W when
> idle.  IMHO, that's not really very significant anymore, especially when
> your CPU eats 20-70W.  Both of these numbers are way better then drives
> only a generation or two back -- last year's ST39175 (9 GB, 7200 RPM) drew
> 9.75W when idle.

I've just done some more research on this, IBM Deskstar workstation drives 
40G:
7200RPM - 6.7W idle
5400RPM - 4.9W idle

IBM UltraStar server drives 36G:
Ultra 160SCSI 10K rpm - 7.4W idle
FCAL 10K rpm - 9.4W idle
Ultra 160SCSI 7200rpm - 8.9W idle


These results surprise me.  It seems that the only way of significantly 
reducing power by using a lower speed is when using Deskstar IDE drives.

Also I am curious as to why a drive that uses FC-AL will take so much more 
power because of it!
My previous message on this topic was based on information that is (now) 
obviously out of date.

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