| Author |
Message |
TwistedPair
Guest
|
 Posted:
Tue Dec 21, 2004 9:37 pm Post subject:
Disable write caching |
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All,
Would it be a true statement to say that write-caching could lead to
corruption on an Exchange 2003 server in a clustered environment?
Thanks,
Pair |
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| Back to top |
|
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Rodney R. Fournier [MVP]
Guest
|
| Posted:
Tue Dec 21, 2004 9:47 pm Post subject:
Re: Disable write caching |
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|
It used to be the Microsoft recommendation, but not anymore. The answer is
it depends on the hardware, it is battery backed up? If your controller can
keep data through a power lose, then write-caching is a very good thing to
use. If your controller can't recover data from a surprise shutdown or power
failure, then DO NOT use write-caching, because you will indeed corrupt the
data in ANY Exchange environment - clustered or not.
Same can be said of Active Directory, SQL Server 2000, WINS, DHCP, etc.
Though much lesser for the smaller databases.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"TwistedPair" <twistedpair@mail.com> wrote in message
news:ed%23G6L35EHA.3644@tk2msftngp13.phx.gbl...
| Quote: | All,
Would it be a true statement to say that write-caching could lead to
corruption on an Exchange 2003 server in a clustered environment?
Thanks,
Pair
|
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| Back to top |
|
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TwistedPair
Guest
|
| Posted:
Tue Dec 21, 2004 10:05 pm Post subject:
Re: Disable write caching |
|
|
Based on your answer, I am going to surmise it is a bad idea in my case
then. Instead of having a shared disk array, I have a replicated disk array
using Geocluster (it fools MSCS into thinking I have a shared disk, when in
reality it is two nodes which keep each other's data synchronized). Works
great, but if I have write caching running on both servers, it isn't shared
at all. When one server fails over, I am sure that could cause corruption.
Instead of the cache being on a single shared unit, it is running on two
separate units, and therefore not synchronized. I am assuming this could be
VERY bad.
Thanks,
Pair
"Rodney R. Fournier [MVP]" <rod@die.spam.die.nw-america.com> wrote in
message news:%23qPqcR35EHA.3416@TK2MSFTNGP09.phx.gbl...
| Quote: | It used to be the Microsoft recommendation, but not anymore. The answer is
it depends on the hardware, it is battery backed up? If your controller
can keep data through a power lose, then write-caching is a very good
thing to use. If your controller can't recover data from a surprise
shutdown or power failure, then DO NOT use write-caching, because you will
indeed corrupt the data in ANY Exchange environment - clustered or not.
Same can be said of Active Directory, SQL Server 2000, WINS, DHCP, etc.
Though much lesser for the smaller databases.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"TwistedPair" <twistedpair@mail.com> wrote in message
news:ed%23G6L35EHA.3644@tk2msftngp13.phx.gbl...
All,
Would it be a true statement to say that write-caching could lead to
corruption on an Exchange 2003 server in a clustered environment?
Thanks,
Pair
|
|
|
| Back to top |
|
|
Rodney R. Fournier [MVP]
Guest
|
| Posted:
Tue Dec 21, 2004 10:12 pm Post subject:
Re: Disable write caching |
|
|
Agreed, DO NOT Turn it on! Smart move asking about this one. I have had
several customers kill DBs with write-caching on.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"TwistedPair" <twistedpair@mail.com> wrote in message
news:%23p0Jqb35EHA.2568@TK2MSFTNGP11.phx.gbl...
| Quote: | Based on your answer, I am going to surmise it is a bad idea in my case
then. Instead of having a shared disk array, I have a replicated disk
array using Geocluster (it fools MSCS into thinking I have a shared disk,
when in reality it is two nodes which keep each other's data
synchronized). Works great, but if I have write caching running on both
servers, it isn't shared at all. When one server fails over, I am sure
that could cause corruption. Instead of the cache being on a single shared
unit, it is running on two separate units, and therefore not synchronized.
I am assuming this could be VERY bad.
Thanks,
Pair
"Rodney R. Fournier [MVP]" <rod@die.spam.die.nw-america.com> wrote in
message news:%23qPqcR35EHA.3416@TK2MSFTNGP09.phx.gbl...
It used to be the Microsoft recommendation, but not anymore. The answer
is it depends on the hardware, it is battery backed up? If your
controller can keep data through a power lose, then write-caching is a
very good thing to use. If your controller can't recover data from a
surprise shutdown or power failure, then DO NOT use write-caching,
because you will indeed corrupt the data in ANY Exchange environment -
clustered or not.
Same can be said of Active Directory, SQL Server 2000, WINS, DHCP, etc.
Though much lesser for the smaller databases.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"TwistedPair" <twistedpair@mail.com> wrote in message
news:ed%23G6L35EHA.3644@tk2msftngp13.phx.gbl...
All,
Would it be a true statement to say that write-caching could lead to
corruption on an Exchange 2003 server in a clustered environment?
Thanks,
Pair
|
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| Back to top |
|
|
Russ Kaufmann [MCT]
Guest
|
| Posted:
Tue Dec 21, 2004 11:46 pm Post subject:
Re: Disable write caching |
|
|
"TwistedPair" <twistedpair@mail.com> wrote in message
news:ed%23G6L35EHA.3644@tk2msftngp13.phx.gbl...
| Quote: | All,
Would it be a true statement to say that write-caching could lead to
corruption on an Exchange 2003 server in a clustered environment?
|
It was a known problem with 5.5 and also was a problem that I ran into
several times with 2000 and 2003. Battery backups didn't make a difference
in the cases that I saw.
I recommend not using write back caching for the transaction logs. It seems
to be the root of many evils. I have not seen the same problem with the DB,
though, just the transaction logs. |
|
| Back to top |
|
|
Russ Kaufmann [MCT]
Guest
|
| Posted:
Tue Dec 21, 2004 11:47 pm Post subject:
Re: Disable write caching |
|
|
"TwistedPair" <twistedpair@mail.com> wrote in message
news:%23p0Jqb35EHA.2568@TK2MSFTNGP11.phx.gbl...
| Quote: | Based on your answer, I am going to surmise it is a bad idea in my case
then. Instead of having a shared disk array, I have a replicated disk
array using Geocluster (it fools MSCS into thinking I have a shared disk,
when in reality it is two nodes which keep each other's data
synchronized). Works great, but if I have write caching running on both
servers, it isn't shared at all. When one server fails over, I am sure
that could cause corruption. Instead of the cache being on a single shared
unit, it is running on two separate units, and therefore not synchronized.
I am assuming this could be VERY bad.
|
Yes, it could be very bad. However, I really don't know enough about
Geocluster to verify. |
|
| Back to top |
|
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Rodney R. Fournier [MVP]
Guest
|
| Posted:
Tue Dec 21, 2004 11:57 pm Post subject:
Re: Disable write caching |
|
|
Not according to HP at Tech Ed San Diego this year, he said to turn it on
now a days. Nothing about T-Log issues, which I have never seen. Maybe
someone from Microsoft will weigh in.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"Russ Kaufmann [MCT]" <russ@exchangemct.nospam.com> wrote in message
news:Oxx80S45EHA.1296@TK2MSFTNGP10.phx.gbl...
| Quote: | "TwistedPair" <twistedpair@mail.com> wrote in message
news:ed%23G6L35EHA.3644@tk2msftngp13.phx.gbl...
All,
Would it be a true statement to say that write-caching could lead to
corruption on an Exchange 2003 server in a clustered environment?
It was a known problem with 5.5 and also was a problem that I ran into
several times with 2000 and 2003. Battery backups didn't make a difference
in the cases that I saw.
I recommend not using write back caching for the transaction logs. It
seems to be the root of many evils. I have not seen the same problem with
the DB, though, just the transaction logs.
|
|
|
| Back to top |
|
|
Scott Schnoll [MSFT]
Guest
|
| Posted:
Wed Dec 22, 2004 12:10 am Post subject:
Re: Disable write caching |
|
|
I'll weigh in. :-)
If you run an unprotected write-back cache against the log drive, logical
corruption may occur. An unprotected write-back cache is a cache where data
is lost if the electricity is interrupted (e.g., no battery backup). When a
write operation to the log disk is complete, Extensible Storage Engine 98
(ESE 98) commits the transaction and makes the data durable on the disk. Any
durable updates persist even if the computer stops responding immediately
after the transaction is committed because the system's restart procedure
completes any unfinished operations that the transaction requires. After the
data is written to the log disk, ESE 98 is free to flush the corresponding
page to the database disk. If the data was never written to the log disk,
the same problem occurs and the recovery process cannot restore the database
to the state that it was in before the database was corrupted. Therefore,
the database remains corrupted.
The problems that may occur when you use write-back caching do not prevent
you from using write-back caching. However, because the potential for
problems does exist, you must make sure that the data in the cache is
correctly protected with a battery backup, with error checking, with error
correction, and with sound operational procedures.
Please see the following references on this:
http://support.microsoft.com/kb/288700
http://support.microsoft.com/kb/828068
http://support.microsoft.com/kb/329232
Hope this helps.
--
Scott Schnoll
This posting is provided "AS IS" with no warranties, and confers no
rights. Please do not send email directly to this alias. This alias is for
newsgroup
purposes only.
"Rodney R. Fournier [MVP]" <rod@die.spam.die.nw-america.com> wrote in
message news:eoLcQa45EHA.3648@TK2MSFTNGP11.phx.gbl...
| Quote: | Not according to HP at Tech Ed San Diego this year, he said to turn it on
now a days. Nothing about T-Log issues, which I have never seen. Maybe
someone from Microsoft will weigh in.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"Russ Kaufmann [MCT]" <russ@exchangemct.nospam.com> wrote in message
news:Oxx80S45EHA.1296@TK2MSFTNGP10.phx.gbl...
"TwistedPair" <twistedpair@mail.com> wrote in message
news:ed%23G6L35EHA.3644@tk2msftngp13.phx.gbl...
All,
Would it be a true statement to say that write-caching could lead to
corruption on an Exchange 2003 server in a clustered environment?
It was a known problem with 5.5 and also was a problem that I ran into
several times with 2000 and 2003. Battery backups didn't make a
difference in the cases that I saw.
I recommend not using write back caching for the transaction logs. It
seems to be the root of many evils. I have not seen the same problem with
the DB, though, just the transaction logs.
|
|
|
| Back to top |
|
|
Russ Kaufmann [MCT]
Guest
|
| Posted:
Wed Dec 22, 2004 12:20 am Post subject:
Re: Disable write caching |
|
|
"Rodney R. Fournier [MVP]" <rod@die.spam.die.nw-america.com> wrote in
message news:eoLcQa45EHA.3648@TK2MSFTNGP11.phx.gbl...
| Quote: | Not according to HP at Tech Ed San Diego this year, he said to turn it on
now a days. Nothing about T-Log issues, which I have never seen. Maybe
someone from Microsoft will weigh in.
|
I do admit it was a problem with past arrays more so than current
technology. The issue was how the battery backed up the write back cache.
I would guess it is not near the problem today that it was a couple of years
ago. |
|
| Back to top |
|
|
Rodney R. Fournier [MVP]
Guest
|
| Posted:
Wed Dec 22, 2004 12:27 am Post subject:
Re: Disable write caching |
|
|
Ok, so you know I am not crazy do this. Go to Google and use this -
site:hp.com write-caching Exchange.
Notice all the CURRENT articles mention to set write-caching to 100%.
Examples:
http://h71019.www7.hp.com/aa_downloads/6/100/225/1/73833.pdf Page 28 100%
write
http://h18002.www1.hp.com/solutions/messaging/medium_business_pop.html - 642
controller with 100% write-caching.
Lastly, HP Exchange 2000/2003 Best Practices -
http://h71019.www7.hp.com/aa_downloads/6/100/225/1/73843.pdf Page 24.
Note: I am not really replying to Scott or Microsoft, but more to explain my
position.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"Scott Schnoll [MSFT]" <scschnol@online.microsoft.com> wrote in message
news:OE3BRh45EHA.1264@TK2MSFTNGP12.phx.gbl...
| Quote: | I'll weigh in. :-)
If you run an unprotected write-back cache against the log drive, logical
corruption may occur. An unprotected write-back cache is a cache where
data is lost if the electricity is interrupted (e.g., no battery backup).
When a write operation to the log disk is complete, Extensible Storage
Engine 98 (ESE 98) commits the transaction and makes the data durable on
the disk. Any durable updates persist even if the computer stops
responding immediately after the transaction is committed because the
system's restart procedure completes any unfinished operations that the
transaction requires. After the data is written to the log disk, ESE 98 is
free to flush the corresponding page to the database disk. If the data was
never written to the log disk, the same problem occurs and the recovery
process cannot restore the database to the state that it was in before the
database was corrupted. Therefore, the database remains corrupted.
The problems that may occur when you use write-back caching do not prevent
you from using write-back caching. However, because the potential for
problems does exist, you must make sure that the data in the cache is
correctly protected with a battery backup, with error checking, with error
correction, and with sound operational procedures.
Please see the following references on this:
http://support.microsoft.com/kb/288700
http://support.microsoft.com/kb/828068
http://support.microsoft.com/kb/329232
Hope this helps.
--
Scott Schnoll
This posting is provided "AS IS" with no warranties, and confers no
rights. Please do not send email directly to this alias. This alias is for
newsgroup
purposes only.
"Rodney R. Fournier [MVP]" <rod@die.spam.die.nw-america.com> wrote in
message news:eoLcQa45EHA.3648@TK2MSFTNGP11.phx.gbl...
Not according to HP at Tech Ed San Diego this year, he said to turn it on
now a days. Nothing about T-Log issues, which I have never seen. Maybe
someone from Microsoft will weigh in.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"Russ Kaufmann [MCT]" <russ@exchangemct.nospam.com> wrote in message
news:Oxx80S45EHA.1296@TK2MSFTNGP10.phx.gbl...
"TwistedPair" <twistedpair@mail.com> wrote in message
news:ed%23G6L35EHA.3644@tk2msftngp13.phx.gbl...
All,
Would it be a true statement to say that write-caching could lead to
corruption on an Exchange 2003 server in a clustered environment?
It was a known problem with 5.5 and also was a problem that I ran into
several times with 2000 and 2003. Battery backups didn't make a
difference in the cases that I saw.
I recommend not using write back caching for the transaction logs. It
seems to be the root of many evils. I have not seen the same problem
with the DB, though, just the transaction logs.
|
|
|
| Back to top |
|
|
Rodney R. Fournier [MVP]
Guest
|
| Posted:
Wed Dec 22, 2004 12:30 am Post subject:
Re: Disable write caching |
|
|
Agreed, but we both agree you need to test and fully understand your
hardware and what it can and can't do.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"Russ Kaufmann [MCT]" <russ@exchangemct.nospam.com> wrote in message
news:Omz70l45EHA.3120@TK2MSFTNGP12.phx.gbl...
| Quote: | "Rodney R. Fournier [MVP]" <rod@die.spam.die.nw-america.com> wrote in
message news:eoLcQa45EHA.3648@TK2MSFTNGP11.phx.gbl...
Not according to HP at Tech Ed San Diego this year, he said to turn it on
now a days. Nothing about T-Log issues, which I have never seen. Maybe
someone from Microsoft will weigh in.
I do admit it was a problem with past arrays more so than current
technology. The issue was how the battery backed up the write back cache.
I would guess it is not near the problem today that it was a couple of
years ago.
|
|
|
| Back to top |
|
|
Scott Schnoll [MSFT]
Guest
|
| Posted:
Wed Dec 22, 2004 12:44 am Post subject:
Re: Disable write caching |
|
|
Yes, and they all call-out specifically using battery backed caches.
--
Scott Schnoll
This posting is provided "AS IS" with no warranties, and confers no
rights. Please do not send email directly to this alias. This alias is for
newsgroup
purposes only.
"Rodney R. Fournier [MVP]" <rod@die.spam.die.nw-america.com> wrote in
message news:uyY4Hr45EHA.3596@TK2MSFTNGP12.phx.gbl...
| Quote: | Ok, so you know I am not crazy do this. Go to Google and use this -
site:hp.com write-caching Exchange.
Notice all the CURRENT articles mention to set write-caching to 100%.
Examples:
http://h71019.www7.hp.com/aa_downloads/6/100/225/1/73833.pdf Page 28 100%
write
http://h18002.www1.hp.com/solutions/messaging/medium_business_pop.html -
642 controller with 100% write-caching.
Lastly, HP Exchange 2000/2003 Best Practices -
http://h71019.www7.hp.com/aa_downloads/6/100/225/1/73843.pdf Page 24.
Note: I am not really replying to Scott or Microsoft, but more to explain
my position.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"Scott Schnoll [MSFT]" <scschnol@online.microsoft.com> wrote in message
news:OE3BRh45EHA.1264@TK2MSFTNGP12.phx.gbl...
I'll weigh in. :-)
If you run an unprotected write-back cache against the log drive, logical
corruption may occur. An unprotected write-back cache is a cache where
data is lost if the electricity is interrupted (e.g., no battery backup).
When a write operation to the log disk is complete, Extensible Storage
Engine 98 (ESE 98) commits the transaction and makes the data durable on
the disk. Any durable updates persist even if the computer stops
responding immediately after the transaction is committed because the
system's restart procedure completes any unfinished operations that the
transaction requires. After the data is written to the log disk, ESE 98
is free to flush the corresponding page to the database disk. If the data
was never written to the log disk, the same problem occurs and the
recovery process cannot restore the database to the state that it was in
before the database was corrupted. Therefore, the database remains
corrupted.
The problems that may occur when you use write-back caching do not
prevent you from using write-back caching. However, because the potential
for problems does exist, you must make sure that the data in the cache is
correctly protected with a battery backup, with error checking, with
error correction, and with sound operational procedures.
Please see the following references on this:
http://support.microsoft.com/kb/288700
http://support.microsoft.com/kb/828068
http://support.microsoft.com/kb/329232
Hope this helps.
--
Scott Schnoll
This posting is provided "AS IS" with no warranties, and confers no
rights. Please do not send email directly to this alias. This alias is
for newsgroup
purposes only.
"Rodney R. Fournier [MVP]" <rod@die.spam.die.nw-america.com> wrote in
message news:eoLcQa45EHA.3648@TK2MSFTNGP11.phx.gbl...
Not according to HP at Tech Ed San Diego this year, he said to turn it
on now a days. Nothing about T-Log issues, which I have never seen.
Maybe someone from Microsoft will weigh in.
Cheers,
Rod
MVP - Windows Server - Clustering
http://www.nw-america.com - Clustering
http://msmvps.com/clustering - Blog
"Russ Kaufmann [MCT]" <russ@exchangemct.nospam.com> wrote in message
news:Oxx80S45EHA.1296@TK2MSFTNGP10.phx.gbl...
"TwistedPair" <twistedpair@mail.com> wrote in message
news:ed%23G6L35EHA.3644@tk2msftngp13.phx.gbl...
All,
Would it be a true statement to say that write-caching could lead to
corruption on an Exchange 2003 server in a clustered environment?
It was a known problem with 5.5 and also was a problem that I ran into
several times with 2000 and 2003. Battery backups didn't make a
difference in the cases that I saw.
I recommend not using write back caching for the transaction logs. It
seems to be the root of many evils. I have not seen the same problem
with the DB, though, just the transaction logs.
|
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|
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|
|
|
|
|
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