Re: [SLUG] LVM

[Tony Sceats <tony@xxxxxxxxxxx>]

not really on topic, but a fun little site detailing some disk vibrating
issues

http://blogs.sun.com/brendan/entry/unusual_disk_latency



On Tue, Jun 15, 2010 at 3:10 PM, james <jam@xxxxxxxxx> wrote:

> On Tuesday 15 June 2010 12:15:52 you wrote:
> > On Tue, Jun 15, 2010 at 11:14:38AM +0800, james wrote:
> > > The stuff  below is interesting and a reference, but this highlights my
> > > favourite rant: Seagate's 'ATA more than an interface' says multiple
> > > disks in a machine *will* result in a higher failure rate, maybe much
> > > higher.
> >
> > Due to heat, or what? That paper seems to concern itself primarily with
> the
> > differences between PS (personal storage) drives and ES (enterprise
> >  storage), in order to justify why the SCSI drives have so much higher
> cost
> >  per bit.
>
> The bit that says:
> Disk#1 seeks knocking Disk#2, Disk#3 off track
> so
> Disk#2 seeks knocking (mechanical coupling) Disk#1 off track
> so
> Disk#1 seeks again
> etc
>
> my own experience is that n-disk arrays fail more than n times 1 disk
> but that is oh so subjective, and so subject to the ravages of stats.
>
> James
>
> > The only mention I could see about multiple disks affecting failure rate
> > was "A high density server rack with many disc drives grouped close
> >  together may experience much higher temperatures than a single drive
> >  mounted in a desktop computer". Nothing about whether multiple disks in
> a
> >  machine affect failure rate for any reason other than high temperature
> >  (which is usually controlled in server environments).
> >
> > > So raid is a less worse option than LVM. Heed the advice in slug talks
> > > about backup (Sorry Sonia and Margurite, I don't remember who presented
> > > them)
> >
> > Yes.
> >
> > > It is possible, but not likely that *every* file on your disks is
> > > distributed over all 3 disks, so worst cast is that you lost 1/3 of
> every
> > > file you have.
> >
> > Only if the Logical Volume is defined with striping (the -i argument to
> >  lvcreate).
> >
> > Rule #1 is always ... make backups.
> >
> > After that:
> >
> > - RAID1 can reduce the impact of a single-drive failure
> >
> > - RAID5 will increase the impact of failures
> >
> > - When combining multiple disks into a large Volume Group (VG), it is
> >  possible to create Logical Volumes within the VG so that they do not
> span
> >  physical devices. That way, if a disk dies (or 2, in a RAID1 setup) the
> >  entire VG contents will not be lost, only those filesystems on the
> failing
> >  devices. Hence it is a good idea to make multiple filesystems sized
> >  according to need.
> >
> > - Make multiple types of backups: backup to HDD (on a different server),
> >  offsite backup, Internet backup, incremental backups, DVD backups,
> >  external HDDs are dirt cheap these days.
> >
> > - Separate data according to importance and increase the redundancy level
> >  for the most important data. Data which is unimportant or can be
> recreated
> >  need not be backed up at all. Precious data might have multiple backups
> to
> >  onsite, offsite and write-once media.
> >
> > Nick.
> >
> --
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