On Sat, Mar 12, 2005 at 02:49:45AM +1300, Michael Honeyfield wrote:
I am just curious the reasoning behind using lvm as the default partitioning method in the anaconda version shipped with FC3.
LVM is good.
On a desktop PC with a single disk? Makes little sense.
Not disputing the fact that lvm is good or bad, asking for the reasoning to making it the default partitioning method.
Cheers
Mike
On Sat, Mar 12, 2005 at 02:54:05AM +1300, Michael Honeyfield wrote:
On Sat, Mar 12, 2005 at 02:49:45AM +1300, Michael Honeyfield wrote:
I am just curious the reasoning behind using lvm as the default partitioning method in the anaconda version shipped with FC3.
LVM is good.
On a desktop PC with a single disk? Makes little sense.
Oh, it makes a lot of sense. To my usual utilization of a desktop system, at least.
Not disputing the fact that lvm is good or bad, asking for the reasoning to making it the default partitioning method.
It makes fixed partitioning go away, making it easy to change partitions on the fly without having to reboot systems and/or use a rescue disc.
Any *problem* with it that may make it undesirable to a desktop system?
lmf
PS: this is not an authoritative answer on the reasons if using lvm by default. I don't know exactly. I believe it has to do with no static partitions and support for ext3 online resizing on the kernel.
On Fri 11 Mar 2005 13:54, Michael Honeyfield wrote:
LVM is good.
On a desktop PC with a single disk? Makes little sense.
I agree.
Also, what is the probability of a disk error causing serious trouble, compared with classical partitions?
On Fri, 2005-03-11 at 17:05 +0000, Timothy Murphy wrote:
On Fri 11 Mar 2005 13:54, Michael Honeyfield wrote:
LVM is good.
On a desktop PC with a single disk? Makes little sense.
I agree.
Also, what is the probability of a disk error causing serious trouble, compared with classical partitions?
Uh, exactly the same?
To elaborate, I'll assume the task which we aim to determine probability of failure based only upon disk errors is "booting the system to the point where init is executed".
Given that, here's basically what it is without LVM. The numbers are very approximate.
boot_sectors is how many sectors BIOS must read to boot anything (1000) grub_sectors is for grub.conf (2) and stage2 (200) kernel_sectors is vmlinuz (3000) and initrd (800) fs_sectors is fs metadata, i.e. superblock+dirents+inodes (1000) sector_p are the probability of a sector failing catastrophically.
p0 = probability of catastrophic disk failure during early boot = probability of failure in a period nearish 5 minutes = ( boot_sectors + grub_config_sectors + kernel_sectors + fs_metadata_sectors ) * sector_p = 1000+2+200+3000+800+1000) * sector_p = 5202 * sector_p
sector_p is *incredibly* small, because most failures on modern disks are correctable read failures. A correctable read failure will cause the sector to be remapped, and so sectors likely to experience catastrophe are typically not in use *at all*.
The MTBF of a random seagate drive google told me about is 1200000 hours, which means the probability of failure during an hour to be 1/(1200000 - previous_runtime_hours), and the probability of failure for a 5 minute period to be 1/(14400000 - previous_runtime_5_minute_periods). That's the mean time, so take it with a grain of salt, but it's the best we're going to do.
So p0 is roughly 5202/14400000 .
If we now consider the LVM setup we're using by default (i.e. / and swap on LVM, /boot on /dev/hda1), still with a single disk, that becomes:
p1 = p0 + lvm_metadata_sectors*sector_p = 5202*sector_p + 100*sector_p = 5302 * sector_p
Which is to say, the difference is zilch.
So in 14400000 boots, 5300 of them will be failures, as opposed to 5200 of them the classical way. Roughly.
I hope you know exactly how meaningless this number is.
On Fri 11 Mar 2005 20:44, Peter Jones wrote:
So in 14400000 boots, 5300 of them will be failures, as opposed to 5200 of them the classical way. Roughly.
I didn't understand your calculation, but your conclusion does not tally with my experience. You are saying that 1 in 3000 boots will fail. In my case this would mean my laptop would fail to boot about once every 5 years.
Actually it fails at least once a week. I'm sure this is not due to a "catastrophic disk failure". (It is probably due to a bad connection. This is a 4-year old Sony Picturebook.)
If as you say this is no more or less likely to occur with LVM then this would not be a cause for concern.
anaconda-devel@lists.fedoraproject.org
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Luciano Miguel Ferreira Rocha -
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Peter Jones -
Timothy Murphy