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Old 02-28-2010, 11:15 PM
Stephen Harris
 
Default puzzling md error ?

On Sun, Feb 28, 2010 at 02:37:13PM -0800, John R Pierce wrote:
> And how do I know all these mirror data mismatches are Swap? does not
> each mismatch mean the mirrors disagree, which means one of them is
> wrong. Which one? since they aren't timestamped or checksummed (like

This thread is very timely. I updated my C5.3 to 5.4 last week (not
sure why it took me so long) and this morning noticed my raid5 was
resyncing. 5*1Tbyte disks. The resync took...
Feb 28 04:22:02 mercury kernel: md: syncing RAID array md3
Feb 28 16:27:06 mercury kernel: md: md3: sync done.

Performance was bad during this time. Not terrible from an interactive
point of view, but a job that normally run from 4am to 10am didn't finish
until 3pm.

I like the concept of checking the disks are good, but it really
sounds like there are practical problems (false positives, performance
degregation) .

So I think /etc/sysconfig/raid-check is going to read
ENABLED=no

--

rgds
Stephen
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Old 03-01-2010, 12:04 AM
Ross Walker
 
Default puzzling md error ?

On Feb 28, 2010, at 7:15 PM, Stephen Harris <lists@spuddy.org> wrote:

> On Sun, Feb 28, 2010 at 02:37:13PM -0800, John R Pierce wrote:
>> And how do I know all these mirror data mismatches are Swap? does
>> not
>> each mismatch mean the mirrors disagree, which means one of them is
>> wrong. Which one? since they aren't timestamped or checksummed
>> (like
>
> This thread is very timely. I updated my C5.3 to 5.4 last week (not
> sure why it took me so long) and this morning noticed my raid5 was
> resyncing. 5*1Tbyte disks. The resync took...
> Feb 28 04:22:02 mercury kernel: md: syncing RAID array md3
> Feb 28 16:27:06 mercury kernel: md: md3: sync done.
>
> Performance was bad during this time. Not terrible from an
> interactive
> point of view, but a job that normally run from 4am to 10am didn't
> finish
> until 3pm.
>
> I like the concept of checking the disks are good, but it really
> sounds like there are practical problems (false positives, performance
> degregation) .
>
> So I think /etc/sysconfig/raid-check is going to read
> ENABLED=no

It would be nice if the mismatch_cnt could be compared to a count of
aborted writes and only resync if they differ, but mismatch_cnt
persists and aborted writes is only maintained since last reboot.

Ideally the md raid code needs to make the writes completely atomic,
so they either complete on all members or none and not allow an abort
task to preempt a write in progress.

-Ross

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Old 03-01-2010, 10:56 AM
JohnS
 
Default puzzling md error ?

On Sun, 2010-02-28 at 14:37 -0800, John R Pierce wrote:
> Clint Dilks wrote:
> > SWAP inside LVM is fine in my experience. Personally I consider this a
> > benign error and generally ignore it unless the mismatch count is very high
>
> And how do I know all these mirror data mismatches are Swap? does not
> each mismatch mean the mirrors disagree, which means one of them is
> wrong. Which one? since they aren't timestamped or checksummed (like
> vxvm, zfs do), I am playing 'data maybe'. As someone who adminstrates
> database servers, i have a real problem with that.
>
> btw, this is centos 5.4+latest x86_64, its primarily running postgres,
> and our inhouse java middleware apps. and was going to be a oracle grid
> operations server.
----

Then any reason to not run the PERC in the 2850? Non of my DB machines
run SWAP period. My thoughts on Linux swap is if I were to use it, it
can't keep up the sync pace, been there.

I realize I say no swap but with MS DesktopEngine and SQL-CEServer I use
swap.

John

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Old 03-01-2010, 08:02 PM
John R Pierce
 
Default puzzling md error ?

JohnS wrote:
> Then any reason to not run the PERC in the 2850? Non of my DB machines
> run SWAP period. My thoughts on Linux swap is if I were to use it, it
> can't keep up the sync pace, been there.
>
>

these 2850 have only JBOD SCSI. PERC was an option, i didn't buy these,
I inherited them.

> I realize I say no swap but with MS DesktopEngine and SQL-CEServer I use
> swap.
>

The oracle installer complains if you don't have swap >= main memory.
I realize I can choose to ignore that.


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Old 03-01-2010, 09:06 PM
JohnS
 
Default puzzling md error ?

On Mon, 2010-03-01 at 13:02 -0800, John R Pierce wrote:
> JohnS wrote:
> > Then any reason to not run the PERC in the 2850? Non of my DB machines
> > run SWAP period. My thoughts on Linux swap is if I were to use it, it
> > can't keep up the sync pace, been there.
> >
> >
>
> these 2850 have only JBOD SCSI. PERC was an option, i didn't buy these,
> I inherited them.
>
> > I realize I say no swap but with MS DesktopEngine and SQL-CEServer I use
> > swap.
> >
>
> The oracle installer complains if you don't have swap >= main memory.
> I realize I can choose to ignore that.
---
And when I see Oracle I complain also.. :-) God, have you priced
Oracle EHR App Stack?

John

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Old 03-03-2010, 06:01 PM
Les Mikesell
 
Default puzzling md error ?

On 2/28/2010 6:15 PM, Stephen Harris wrote:
> On Sun, Feb 28, 2010 at 02:37:13PM -0800, John R Pierce wrote:
>> And how do I know all these mirror data mismatches are Swap? does not
>> each mismatch mean the mirrors disagree, which means one of them is
>> wrong. Which one? since they aren't timestamped or checksummed (like
>
> This thread is very timely. I updated my C5.3 to 5.4 last week (not
> sure why it took me so long) and this morning noticed my raid5 was
> resyncing. 5*1Tbyte disks. The resync took...
> Feb 28 04:22:02 mercury kernel: md: syncing RAID array md3
> Feb 28 16:27:06 mercury kernel: md: md3: sync done.
>
> Performance was bad during this time. Not terrible from an interactive
> point of view, but a job that normally run from 4am to 10am didn't finish
> until 3pm.
>
> I like the concept of checking the disks are good, but it really
> sounds like there are practical problems (false positives, performance
> degregation) .
>
> So I think /etc/sysconfig/raid-check is going to read
> ENABLED=no

I agree that is is a fairly surprising behavior change for an
'enterprise' system where the point is mostly to not have surprising
behavior changes. On the other hand it is probably a good thing to do
if you can make the scheduling fit in.

--
Les Mikesell
lesmikesell@gmail.com



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