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