[Centos] Promise raid cards - software raid
William Warren
hescominsoon at emmanuelcomputerconsulting.com
Thu Nov 4 20:04:58 UTC 2004
In my limited experience with linux(i have a firewall using ext3
and a small file server using ext3) power failures have not
negatively impacted the file system. The only thing i did wrong
was forcing fsck which corrupted things into an unrecoverable state.
dan1 wrote:
> 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 <mailto:tmartin at physics.ucsd.edu>
> *Cc:* CentOS at caosity.org <mailto:CentOS at caosity.org>
> *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 at revsharecorp.com>
> > *To:* dan1 <mailto:dan1 at edenpics.com>
> > *Cc:* CentOS at caosity.org <mailto:CentOS at caosity.org>
> <mailto:CentOS at caosity.org>
> > *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
> >
>
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Isa 54:17 No weapon that is formed against thee shall prosper;
and every tongue that shall rise against thee in judgment thou
shalt condemn. This is the heritage of the servants of the LORD,
and their righteousness is of me, saith the LORD.
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