[linux-lvm] multiple volumes..
andewid at tnonline.net
Wed Apr 10 05:16:02 UTC 2002
Woha. Lot's of replies :)
1) Speed is generally not the biggest importance. 5-6MB/s would be
All drives are UDMA 100, and there are 4 UDMA 100 host controllers in
this system. If I want to, I can have 16 drives. The speed varyes
between 25-35MB/s for all drives.
The reason I choose a RAID 5 setup was that one drive could
die (to the point where no data recovery is possible) without loosing
any data. If the system gets very slow, or I might even have to bring
it down to replace the drive, that's fine.
I only need enough security if one drive would fail. Agreed, mirroring
would perhaps be safer, and at least faster when a drive failes. But I
need as much diskspace I can get, and mirroring would consume alot of
> On Wed, 10 Apr 2002 08:01, you wrote:
> but that REQUIRES, that the disks are not
>> You should try to avoid having more than one (active) disk at the same
>> controller at once.
> I've always wondered about this statement.
> The idea AFAIK is that unlike SCSI, IDE has the master drive control the
> slave drive on the same controller.
> 1) This causes problems where the drives are a different
> model/make/manufactuer as the master drive will downgrade the settings of the
> drives (master & slave) to the lowest common denominator; and therefore, the
> speed in this case is affected.
> 2) Having the master drive control the slave drive also causes problems if
> the master fails as then both drives fail or if a drive takes down the chain
> both drives fail.
> 3) maybe a couple of others that I have forgotten at the moment.
> When I was setting up my server at home 1.2GAthlon AsusA7V-133 384M RAM 9x
> IBM 40G drives, 1 Promise Ultra100 & 2 Promise Ultra100TX2 I did a couple of
> I found by using a flaky drive from a previous life (a western digital that
> when it would die would take down the controller) that it didn't matter if
> the drive was a single master on a controller, a master on a shared
> controller or a slave on a shared controller. When the drive would fail - it
> would take the whole machine down with it. The Kernel would not die but it
> would deadlock waiting for interrupts to return and the only way to fix the
> issue was to hard reset. Having the flaky dirve as a standalone drive or as
> part of a software RAID made no difference. So I concluded that at least in
> my setup I gained nothing by only having one IDE drive per controller.
> I also ran bonnie++ tests on a software RAID0 using 4 master only drives
> (hde, hdg, hdi, hdk) and 4 master-slave drives (hde, hdf, hdg, hdh). The
> results of the test were that seek times for the master-slave case were half
> that for the master-master case. Read times did drop but only by about
> .75M/s from 80M/s but the write times improved by about .25-.75M/s from
> 50M/s. So I concluded that at least for my setup it was better to have the
> master-slave case because the loss of read speed was made up by the increase
> in write speed.
> So my final configuration was that hda, hdb were system disks. The RAID5
> used hde, hdg, hdi, hdk with a hot spare hdo and the RAID0 used hdm & hdn.
> Now the tests weren't what I would call conclusive or proper scientific tests
> but I believe they were valid. I've always wondered what others have found
> as what I found seems to fly in the face of common rules of thumb.
> There is a specific mailing list "linux ide"
> <linux-ide-arrays at lists.math.uh.edu> that deal with large IDE arrays so you
> might like to also ask your question there and see what is suggested.
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