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Hello, Terrence.
Thank you for this sharing.
It is very sad that these cards don't provide cache flush in case of power
failure, because it's the main difference I thought between software raid
and hardware raid.
Some people told me that software raid was dangerous because of that fact
(no battery when power fails), and hardware raid would solve this problem.
In this case, to me there is no main advantage to use hardware raid.
Then, I am quite interested be anyone having any experience with software
raid power failures with ext3. Does the filesystem crash often ? And is it
severe ?
Thanks in advance to all,
Daniel
----- Original Message -----
From: Terrence Martin
Cc: CentOS@xxxxxxxxxxx
Sent: Thursday, November 04, 2004 7:47 PM
Subject: Re: [Centos] Promise raid cards
Those cards have no battery backup. When the power goes they are off,
any cached data is gone. However a power failure in my experience is not
a problem, or at least not more of a problem than is to be expected from
ATA disks.
ATA Disk all suffer from write back caching problem. That is you never
really know if data is written to disk. Today many of your ATA drives
are coming with 8MB of cache. That is 8MB of data that could be sitting
in volatile RAM in the event of a power failure. Even a card with a
battery backup will not help you because the disks themselves may hold
some important data. If this is a concern get SCSI or a good UPS with a
shutdown procedure.
You can of course mitigate file system corruption but not data loss with
a good journaled FS. We prefer XFS for anything over 100GB and we run
into the 10's of Terabytes on some systems.
If you system is transaction based (database server) you almost
certainly want a UPS on the whole thing with at least 5-10 minutes,
preferably 20 minutes of battery life. That should give you time to sync
your disks and shut the system down hopefully. You will want to test
this of course.
Terrence
dan1 wrote:
> Thank you, Ajay.
>
> That's useful to me.
> And do you know if the 3ware ATA raid card (7006-2 or 7506-4LP I
> suppose) flushes the disks in case of power failure or do they just
> forget the buffered datas so that the filesystem crashes afterwards ?
> (i.e. do they have a capacitor to hold the datas up to the moment they
> are all written). I will have a remote reboot (power failure like)
> that I might use quite often and I know this is no problems with ext3
> filesystem on 1 IDE disk only (I made some tests), but is it the same
> reliability with this 3ware raid card for power failures ?
>
> Thanks a lot for sharing your experience !
>
> Daniel
>
>
>
> ----- Original Message -----
> *From:* Ajay Sharma <mailto:ssharma@xxxxxxxxxxxxxxxx>
> *To:* dan1 <mailto:dan1@xxxxxxxxxxxx>
> *Cc:* CentOS@xxxxxxxxxxx <mailto:CentOS@xxxxxxxxxxx>
> *Sent:* Thursday, November 04, 2004 5:58 PM
> *Subject:* Re: [Centos] Promise raid cards
>
> dan1 wrote:
>
> > I would like to know if promise RAID cards are compatible with
> CentOS /
> > RHEL ?
> > I have seen that only SATA is supported on the RHEL hardware
> > compatibility list. The other ATA raid cards seems not to be
> compatible.
> > They give source code and promise grants compatibility with
> RedHat 8 and
> > 9 but not RHEL.
> >
> > I would like to know if somebody tried a ATA raid card like
> Fasttrack
> > TX2000, SX4000, Fasttrack 100 TX2, etc..
> > If you could share me your experience it would be great.
> >
> > My provider says that he had some bad experiences about that
> cards and
> > he doesn't allow me to use CentOS on his promise cards he provides
> > (only), so I cannot have RAID on my server... it's a shame..
>
> I haven't checked recently, but the last time I played with any
> promise
> controller it was a train wreck. I then picked up a 3ware ATA
> RAID card
> and never looked back. It's well supported as the drivers are in
the
> main kernel tree since 2.4. So you install your drives, setup the
> ATA
> raid array in the 3ware bios and when you boot up it's detected as a
> SCSI device. It's the easiest solution out there, so IMO, it's well
> worth the extra money.
>
> --Ajay
>
_______________________________________________
CentOS mailing list
CentOS@xxxxxxxxxxx
http://lists.caosity.org/mailman/listinfo/centos
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<DIV><FONT face=3DArial size=3D2>Hello, Terrence.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Thank you for this =
sharing.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>It is very sad that these cards don't =
provide cache=20
flush in case of power failure, because it's the main difference I =
thought=20
between software raid and hardware raid.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Some people told me that software raid =
was=20
dangerous because of that fact (no battery when power fails), and =
hardware raid=20
would solve this problem. In this case, to me there is no main =
advantage to use hardware raid.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Then, I am quite interested be anyone =
having any=20
experience with software raid power failures with ext3. Does the =
filesystem=20
crash often ? And is it severe ?</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Thanks in advance to all,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Daniel</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<BLOCKQUOTE=20
style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A title=3Dtmartin@xxxxxxxxxxxxxxxx=20
href=3D"mailto:tmartin@xxxxxxxxxxxxxxxx";>Terrence Martin</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Cc:</B> <A =
title=3DCentOS@xxxxxxxxxxx=20
href=3D"mailto:CentOS@xxxxxxxxxxx";>CentOS@xxxxxxxxxxx</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Thursday, November 04, =
2004 7:47=20
PM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Re: [Centos] Promise =
raid=20
cards</DIV>
<DIV><BR></DIV>Those cards have no battery backup. When the power goes =
they=20
are off, <BR>any cached data is gone. However a power failure in my =
experience=20
is not <BR>a problem, or at least not more of a problem than is to be =
expected=20
from <BR>ATA disks.<BR><BR>ATA Disk all suffer from write back caching =
problem. That is you never <BR>really know if data is written to disk. =
Today=20
many of your ATA drives <BR>are coming with 8MB of cache. That is 8MB =
of data=20
that could be sitting <BR>in volatile RAM in the event of a power =
failure.=20
Even a card with a <BR>battery backup will not help you because the =
disks=20
themselves may hold <BR>some important data. If this is a concern get =
SCSI or=20
a good UPS with a <BR>shutdown procedure.<BR><BR>You can of course =
mitigate=20
file system corruption but not data loss with <BR>a good journaled FS. =
We=20
prefer XFS for anything over 100GB and we run <BR>into the 10's of =
Terabytes=20
on some systems.<BR><BR>If you system is transaction based (database =
server)=20
you almost <BR>certainly want a UPS on the whole thing with at least =
5-10=20
minutes, <BR>preferably 20 minutes of battery life. That should give =
you time=20
to sync <BR>your disks and shut the system down hopefully. You will =
want to=20
test <BR>this of =
course.<BR><BR>Terrence<BR><BR><BR><BR><BR><BR><BR>dan1=20
wrote:<BR><BR>> Thank you, Ajay.<BR>> <BR>> That's =
useful to=20
me.<BR>> And do you know if the 3ware ATA raid card (7006-2 or =
7506-4LP I=20
<BR>> suppose) flushes the disks in case of power failure or do =
they just=20
<BR>> forget the buffered datas so that the filesystem crashes =
afterwards ?=20
<BR>> (i.e. do they have a capacitor to hold the datas up to the =
moment=20
they <BR>> are all written). I will have a remote reboot (power =
failure=20
like) <BR>> that I might use quite often and I know this is no =
problems=20
with ext3 <BR>> filesystem on 1 IDE disk only (I made some tests), =
but is=20
it the same <BR>> reliability with this 3ware raid card for power =
failures=20
?<BR>> <BR>> Thanks a lot for sharing your experience=20
!<BR>> <BR>> Daniel<BR>> <BR>> =20
<BR>><BR>> ----- Original Message=20
-----<BR>> *From:* Ajay Sharma <<A=20
=
href=3D"mailto:ssharma@xxxxxxxxxxxxxxxx";>mailto:ssharma@xxxxxxxxxxxxxxxx<=
/A>><BR>> =20
*To:* dan1 <<A=20
=
href=3D"mailto:dan1@xxxxxxxxxxxx";>mailto:dan1@xxxxxxxxxxxx</A>><BR>>=
; =20
*Cc:* <A href=3D"mailto:CentOS@xxxxxxxxxxx";>CentOS@xxxxxxxxxxx</A> =
<<A=20
=
href=3D"mailto:CentOS@xxxxxxxxxxx";>mailto:CentOS@xxxxxxxxxxx</A>><BR>&=
gt; =20
*Sent:* Thursday, November 04, 2004 5:58 =
PM<BR>> =20
*Subject:* Re: [Centos] Promise raid=20
cards<BR>><BR>> dan1=20
wrote:<BR>><BR>> > I would like to =
know if=20
promise RAID cards are compatible with<BR>> =
CentOS=20
/<BR>> > RHEL =
?<BR>> =20
> I have seen that only SATA is supported on the RHEL=20
hardware<BR>> > compatibility list. The =
other=20
ATA raid cards seems not to be<BR>> =20
compatible.<BR>> > They give source code =
and=20
promise grants compatibility with<BR>> =
RedHat 8=20
and<BR>> > 9 but not=20
RHEL.<BR>> > =
<BR>> =20
> I would like to know if somebody tried a ATA raid card=20
like<BR>> =
Fasttrack<BR>> =20
> TX2000, SX4000, Fasttrack 100 TX2, =
etc..<BR>> =20
> If you could share me your experience it would be=20
great.<BR>> > =
<BR>> =20
> My provider says that he had some bad experiences about=20
that<BR>> cards =
and<BR>> =20
> he doesn't allow me to use CentOS on his promise cards he=20
provides<BR>> > (only), so I cannot have =
RAID on=20
my server... it's a shame..<BR>><BR>> I =
haven't=20
checked recently, but the last time I played with=20
any<BR>> =
promise<BR>> =20
controller it was a train wreck. I then picked up a 3ware=20
ATA<BR>> RAID =
card<BR>> =20
and never looked back. It's well supported as the drivers are in =
the<BR>> main kernel tree since 2.4. =
So you=20
install your drives, setup the<BR>> =20
ATA<BR>> raid array in the 3ware bios and =
when you=20
boot up it's detected as a<BR>> SCSI =
device. =20
It's the easiest solution out there, so IMO, it's=20
well<BR>> worth the extra=20
money.<BR>><BR>> =20
=
--Ajay<BR>><BR><BR>_______________________________________________<BR>=
CentOS=20
mailing list<BR><A=20
href=3D"mailto:CentOS@xxxxxxxxxxx";>CentOS@xxxxxxxxxxx</A><BR><A=20
=
href=3D"http://lists.caosity.org/mailman/listinfo/centos";>http://lists.ca=
osity.org/mailman/listinfo/centos</A></BLOCKQUOTE></BODY></HTML>
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