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Old 02-10-2010, 05:59 AM
Neil Walker
 
Default 1-Terabyte drives - 4K sector sizes? -> bar performance so far

Iain Buchanan wrote:
> I'm starting to stray OT here, but I'm considering a second-hand Adaptec
> 2420SA - this is real hardware raid right?
>

It's a PCI-X card (not PCI-E). Are you sure that's right for your system?

> If I'm buying drives in the 1Tb size - does this 4k issue affect
> hardware RAID and how do you get around it? (Never set up a HW RAID
> card before)
>

You would need to check with Adaptec. The latest BIOS is 2 years old so
it may not support the latest drives.


Be lucky,

Neil
 
Old 02-10-2010, 06:06 AM
Iain Buchanan
 
Default 1-Terabyte drives - 4K sector sizes? -> bar performance so far

On Tue, 2010-02-09 at 17:27 -0800, Mark Knecht wrote:
> On Tue, Feb 9, 2010 at 4:31 PM, Iain Buchanan <iaindb@netspace.net.au> wrote:
> > On Tue, 2010-02-09 at 14:54 -0800, Mark Knecht wrote:

> >> Frank,
> >> As best I can tell so far none of the Linux tools will tell you
> >> that the sectors are 4K. I had to go to the WD web site and find the
> >> actual drive specs to discover that was true.
> >
> > however if you use dmesg:

> Consider as an alternative "hdparm dash capital eye".

Not sure why you spelt it, but tee hach ae en kay ess!

I knew there was another way somewhere, but it didn't spring to mind
immediately.
--
Iain Buchanan <iaindb at netspace dot net dot au>

Actually, my goal is to have a sandwich named after me.
 
Old 02-10-2010, 06:08 AM
Alan McKinnon
 
Default 1-Terabyte drives - 4K sector sizes? -> bar performance so far

On Wednesday 10 February 2010 01:22:31 Iain Buchanan wrote:
> On Tue, 2010-02-09 at 08:47 +0100, J. Roeleveld wrote:
> > I now only need to figure out the best way to configure LVM over this to
> > get the best performance from it. Does anyone know of a decent way of
> > figuring this out?
> > I got 6 disks in Raid-5.
>
> why LVM? Planning on changing partition size later? LVM is good for
> (but not limited to) non-raid setups where you want one partition over a
> number of disks.
>
> If you have RAID 5 however, don't you just get one large disk out of it?
> In which case you could just create x partitions. You can always use
> parted to resize / move them later.
>
> IMHO recovery from tiny boot disks is easier without LVM too.
>

General observation (not saying that Iain is wrong):

You use RAID to get redundancy, data integrity and performance.

You use lvm to get flexibility, ease of maintenance and the ability to create
volumes larger than any single disk or array. And do it at a reasonable price.

These two things have nothing to do with each other and must be viewed as
such. There are places where RAID and lvm seem to overlap, where one might
think that a feature of one can be used to replace the other. But both really
suck in these overlaps and are not very good at them.

Bottom line: don't try and use RAID or LVM to do $STUFF outside their core
functions. They each do one thing and do it well.


--
alan dot mckinnon at gmail dot com
 
Old 02-10-2010, 06:11 AM
Iain Buchanan
 
Default 1-Terabyte drives - 4K sector sizes? -> bar performance so far

On Wed, 2010-02-10 at 07:31 +0100, Volker Armin Hemmann wrote:
> On Mittwoch 10 Februar 2010, Iain Buchanan wrote:

> > so long as you didn't have any non-detectable disk errors before
> > removing the disk, or any drive failure while one of the drives were
> > removed. And the deterioration in performance while each disk was
> > removed in turn might take more time than its worth. Of course RAID 1
> > wouldn't suffer from this (with >2 disks)...
>
> Raid 6. Two disks can go down.
>

not that I know enough about RAID to comment on this page, but you might
find it interesting:
http://www.baarf.com/
specifically:
http://www.miracleas.com/BAARF/RAID5_versus_RAID10.txt

--
Iain Buchanan <iaindb at netspace dot net dot au>

The executioner is, I hear, very expert, and my neck is very slender.
-- Anne Boleyn
 
Old 02-10-2010, 06:31 AM
Iain Buchanan
 
Default 1-Terabyte drives - 4K sector sizes? -> bar performance so far

On Wed, 2010-02-10 at 06:59 +0000, Neil Walker wrote:
> Iain Buchanan wrote:
> > I'm starting to stray OT here, but I'm considering a second-hand Adaptec
> > 2420SA - this is real hardware raid right?
> >
>
> It's a PCI-X card (not PCI-E). Are you sure that's right for your system?

yes, I have an "old" server tower with everything but the disks (or RAID
controller), so it needs PCI-X.

thanks,
--
Iain Buchanan <iaindb at netspace dot net dot au>

Three minutes' thought would suffice to find this out; but thought is
irksome and three minutes is a long time.
-- A.E. Houseman
 
Old 02-10-2010, 07:37 AM
Volker Armin Hemmann
 
Default 1-Terabyte drives - 4K sector sizes? -> bar performance so far

On Mittwoch 10 Februar 2010, Iain Buchanan wrote:
> On Wed, 2010-02-10 at 07:31 +0100, Volker Armin Hemmann wrote:
> > On Mittwoch 10 Februar 2010, Iain Buchanan wrote:
> > > so long as you didn't have any non-detectable disk errors before
> > > removing the disk, or any drive failure while one of the drives were
> > > removed. And the deterioration in performance while each disk was
> > > removed in turn might take more time than its worth. Of course RAID 1
> > > wouldn't suffer from this (with >2 disks)...
> >
> > Raid 6. Two disks can go down.
>
> not that I know enough about RAID to comment on this page, but you might
> find it interesting:
> http://www.baarf.com/
> specifically:
> http://www.miracleas.com/BAARF/RAID5_versus_RAID10.txt

and that is very wrong:

but if
the drive is going these will not last very long and will run out and SCSI
does NOT report correctable errors back to the OS! Therefore you will not
know the drive is becoming unstable until it is too late and there are no
more replacement sectors and the drive begins to return garbage. [Note
that the recently popular IDE/ATA drives do not (TMK) include bad sector
remapping in their hardware so garbage is returned that much sooner.]

so if the author is wrong on that, what is with the rest of his text?

And why do you think Raid6 was created?

With Raid6 one disk can fail and another return garbage and it is still able
to recover.

Another reason to use raid6 is the error rate. One bit per 10^16 sounds good -
until you are fiddling with terabyte disks.


>Conclusion? For safety and performance favor RAID10 first, RAID3 second,
RAID4 third, and RAID5 last!

and that is just mega stupid. You can google. Or just go straight to
wikipedia, if you don't know why.
 
Old 02-10-2010, 07:43 AM
Volker Armin Hemmann
 
Default 1-Terabyte drives - 4K sector sizes? -> bar performance so far

On Mittwoch 10 Februar 2010, Iain Buchanan wrote:
> On Wed, 2010-02-10 at 07:31 +0100, Volker Armin Hemmann wrote:
> > On Mittwoch 10 Februar 2010, Iain Buchanan wrote:
> > > so long as you didn't have any non-detectable disk errors before
> > > removing the disk, or any drive failure while one of the drives were
> > > removed. And the deterioration in performance while each disk was
> > > removed in turn might take more time than its worth. Of course RAID 1
> > > wouldn't suffer from this (with >2 disks)...
> >
> > Raid 6. Two disks can go down.
>
> not that I know enough about RAID to comment on this page, but you might
> find it interesting:
> http://www.baarf.com/
> specifically:
> http://www.miracleas.com/BAARF/RAID5_versus_RAID10.txt

to give you an example, why raid 1 is not a good choice (and raid 10 too).

You have two disks configured as mirror. They report different blocks. Which one
is the correct one?

And suddenly your system has to guess and you are very out of luck.

Another reason, the author of that text stresses that you have to do more
writes. Newsflash: with Raid1 every single block has to be written twice. So if
you use additional writes against Raid5, Raid1 is instantly disqualified.


You shouldn't listen to people with an agenda.

This is almost as bad as the site that claimed that SATA is much worse than
PATA in every single aspect ...
 
Old 02-10-2010, 09:53 AM
"J. Roeleveld"
 
Default 1-Terabyte drives - 4K sector sizes? -> bar performance so far

On Wednesday 10 February 2010 00:22:31 Iain Buchanan wrote:
> On Tue, 2010-02-09 at 08:47 +0100, J. Roeleveld wrote:
> > I now only need to figure out the best way to configure LVM over this to
> > get the best performance from it. Does anyone know of a decent way of
> > figuring this out?
> > I got 6 disks in Raid-5.
>
> why LVM? Planning on changing partition size later? LVM is good for
> (but not limited to) non-raid setups where you want one partition over a
> number of disks.
>
> If you have RAID 5 however, don't you just get one large disk out of it?
> In which case you could just create x partitions. You can always use
> parted to resize / move them later.
>
> IMHO recovery from tiny boot disks is easier without LVM too.
>

I've been using LVM for quite a while now and prefer it over any existing
partitioning method. Especially as this array is for filesharing and I prefer
to keep different shares on different partitions and the requirements for
sizes are not known at the beginning.

Also, the machine this is in uses Xen virtualisation to consolidate different
servers on a single machine (power-consumption and most servers only need a
lot of resources occasionally) and I already have over 80 LVs just for the
virtual machines themselves. (multiple each, as I don't like a single large
partition for any machine)

As for recovery, I always use "sysrescuecd" (http://www.sysresccd.org) and
this has Raid and LVM support in it. (Same with the Gentoo-livecds)

--
Joost
 
Old 02-10-2010, 09:56 AM
"J. Roeleveld"
 
Default 1-Terabyte drives - 4K sector sizes? -> bar performance so far

On Wednesday 10 February 2010 08:08:44 Alan McKinnon wrote:
> On Wednesday 10 February 2010 01:22:31 Iain Buchanan wrote:
> > On Tue, 2010-02-09 at 08:47 +0100, J. Roeleveld wrote:
> > > I now only need to figure out the best way to configure LVM over this
> > > to get the best performance from it. Does anyone know of a decent way
> > > of figuring this out?
> > > I got 6 disks in Raid-5.
> >
> > why LVM? Planning on changing partition size later? LVM is good for
> > (but not limited to) non-raid setups where you want one partition over a
> > number of disks.
> >
> > If you have RAID 5 however, don't you just get one large disk out of it?
> > In which case you could just create x partitions. You can always use
> > parted to resize / move them later.
> >
> > IMHO recovery from tiny boot disks is easier without LVM too.
>
> General observation (not saying that Iain is wrong):
>
> You use RAID to get redundancy, data integrity and performance.
>
> You use lvm to get flexibility, ease of maintenance and the ability to
> create volumes larger than any single disk or array. And do it at a
> reasonable price.
>
> These two things have nothing to do with each other and must be viewed as
> such. There are places where RAID and lvm seem to overlap, where one might
> think that a feature of one can be used to replace the other. But both
> really suck in these overlaps and are not very good at them.
>
> Bottom line: don't try and use RAID or LVM to do $STUFF outside their core
> functions. They each do one thing and do it well.
>

I completely agree with this.
RAID is for redundancy (Loose a disk, and the system will keep running)
LVM is for flexibility (Resizing/moving partitions using parted or similar
takes time during which the whole system is unusable)

With LVM, I can resize a partition while it is actually in use (eg. write-
activities)
 
Old 02-10-2010, 10:03 AM
Volker Armin Hemmann
 
Default 1-Terabyte drives - 4K sector sizes? -> bar performance so far

On Mittwoch 10 Februar 2010, J. Roeleveld wrote:

> As for recovery, I always use "sysrescuecd" (http://www.sysresccd.org) and
> this has Raid and LVM support in it. (Same with the Gentoo-livecds)

sysrescuecd failed me hard two nights ago. 64bit kernel paniced with stack
corruptions, 32bit kernel took an hour to unpack 300kb from a 20gb tar...

it was pathetic...
 

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