On Fri, Sep 05, 2008 at 12:59:01PM -0700, Jens wrote:
> On 5 Sep., 21:20, "Brian Schrock" <schrock.br...@gmail.com> wrote:
>
> > We use LVM and software raid via md on every server. We use md to run raid
> > 10 arrays and then we use LVM on top of that. We use snapshots to backup our
>
> Hello Brian,
>
> sounds good - what made you stack MD and LVM, and not use LVM's mirror
> feature?
> Any specific reason?
I do the same as brian, md base and lvm on top, my typical setup is
DiskA Partition 1 - 500M (sda1)
DiskA P2 - 10G
DiskA P3 - The rest
DiskB Partition 1 - 500M (sdb1)
DiskB P2 - 10G
DiskB P3 - The rest
..... (for the number of disks)
DiskX Partition 1 - 500M (sdx)
DiskX P2 - 10G
DiskX P3 - The rest
I use
sda1 & sdb1 in a raid1 for /boot (ext2), an old habit, raid1 is the
hardest to f@#k up and it it just hold /boot even harder, I leave enough
room to place rescue stuff there - busbybox and tools
sda2 & sdb2 in a raid1 for / (ext3), shouldn't need more than 10G, used
to use 8G previously, again for its simplicity
Depending on if I have any other disks or not I will make a raid5 (or
raid6) with the sd?3 paritions, if I only have the 2 disks then sda3 &
sdb3 are made into a raid1 and the resultant md is placed as a lvm
physical volume, which I then carve out things like /tmp /var/log /home
swap. This means I can grow them on the fly as needed.
I also looked at lvm mirror, the difference is lvm need a bitmap (which
you have the option of keeping in memory - which is transient). The
overhead of using lvm raid1 did not seem worth it (echo by my results
from googling)
Alex
>
> I have read contradicting reports regarding performance - one said LVM
> mirroring was faster since it read from both disks in parallel, one
> said the same about MD.
> What is your experience?
>
> > mySQL servers and it works great. We do nightly snapshots and rsync/tar that
> > stuff to central on line storage server. Though we do have to issue a lock
> > tables command to our mySQL servers for the duration of the creation of the
> > LVM snapshot, but after the snapshot is created we remove the locks.
>
> That was the idea.
> Do you have to snapshot each LV separately or can you do one snapshot
> for the whole VG?
> Since I only have two disks I'll do a Raid 1 mirror and probably use a
> layout like
>
> md0: root (10G)
> md1: system VG (rest of disk)
> system/swap (probably 4G to start with)
> system/tmp (probably 4G too, tmpfs)
> system/var (10G to start with, will contain MySQL data)
> system/home (rest of disk minus 10G for snapshot data)
>
> This worked quite well so far. But I'm sure once I have the
> flexibility, I will think of another more detailed setup for
> partitioning.
>
> Do you think it's a good idea to put swap and /tmp in the VG?
>
> > For booting, we just use raid 1 on two partitions, no LVM. Debian seems to
> > have no problem with installation, but it does not install grub into both
> > drives mbr. You have to manually do that or if the hdd that does have grub
> > installed fails your system will be unable to boot. Its been a while since I
> > have double checked this, so it may have been fixed.
>
> I have done this with LILO ("raid-extra-boot=") but how do you do it
> with Grub?
> Like this? : http://faq.jensbenecke.de/wiki/SuseSystem
> (scroll down a bit to see the GRUB commands)
>
> > I was just running some bonnie tests yesterday on a test server and here are
> > those results...
> > name file_size putc putc_cpu put_block put_block_cpu rewrite rewrite_cpu
> > getc getc_cpu get_block get_block_cpu seeks seeks_cpu num_files dhcp187
> > 32368M 69293 99 209808 51 66438 13 49501 67 94315 9 777.3 0 16 dhcp187
> > 32368M 68795 97 219512 51 65161 13 49648 67 93097 9 769.1 1 16 dhcp187
> > 32368M 68501 98 222966 53 65132 13 49639 67 94043 9 762.7 1 16 dhcp187
> > 32368M 69498 98 246923 58 63480 12 49937 67 94189 9 785 0 16 dhcp187 32368M
> > 69324 98 230438 55 64656 12 49576 67 94046 9 749 1 16
>
> hm, this does not tell me too much (probably because of bad line
> wrapping).
> did you compare a single disk with a MD setup?
>
> > Brian Schrock,
>
>
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--
"We ended the rule of one of history's worst tyrants, and in so doing, we not only freed the American people, we made our own people more secure."
- George W. Bush
05/03/2003
Crawford, TX
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