Re: [opensuse] 10.2 no RAID to 11.0 RAID 1
Sorry, forgot to change the recipient email address. :(
2008/9/23 Hylton Conacher (ZR1HPC)
2008/9/23 Carlos E. R.
: -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 The Tuesday 2008-09-23 at 12:27 +0200, Hylton Conacher (ZR1HPC) wrote:
No because I've already "been there" and "done that" -- It is IMPOSSIBLE to recover a RAID-1 array that just one day (after properly shutting down the system and not having hardware failures) decided not to boot.
Ahhh, now this is interesting :) The main reason I was creating the RAID1 array was so that if one drive failed, I could receive a message from mdadm, swop out the bad drive and continue working, without losing data.
Of course you can continue. You can even have a third disk as active spare and the system will switch over to it without downtime.
It was only Andrew who had some problem, which at the moment is not fully clear what it was. Ok, Sorry Andrew, you are the bad apple in the mix :)
In view of the above comment, I guess it is time I ordered the 3rd HDD and rather setup RAID5.
You could have the same type of problem. Both raid 1 and raid 5 can withstand the failure of a single disk without downtime, with different approaches. It will depend on the hardware of course, whether you can replace the disk "hot". Hot replacement is not necessary as long as the machine can be powered down, not lose data, have the replacement HDD inserted, and then get restarted and rebuild the array.
HW RAID cards are a MAJOR expense for a home hobbyist who just likes to make sure their data is retrievablein the event of a HDD crash.
In fact, I don't think you need raid at all. I second that as I have read that RAID is not a backup method. A valid backup is a far better replacement for RAID in this instance.
Raid is for minimizing the downtime to zero, for systems that have to be accessible full time. That is not usually the case for home, unless you want to experiment. IMO it is safer to have that second disk as a full backup, updated at least daily via rsync. Now THAT is a SMART idea.
The backup has an advantage: you can recover from a software crash or finger error: the other disk is not mounted, so nothing is written to it "yet". On a raid, both copies would have the same wrong data. The downside is that the machine is going to be a file/print/mail server and while I may have a backup as of yesterday, if I screw up a document, I cannot simply just restore the backup as other email would have been added to the live mail server that would be lost if it was restored from the offline backup. I guess the way around that is to have two rsync jobs being one for the mail directories and the other for only the document directories?
Tnx Carlos for the idea!
Regards Hylton
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2008/9/23 Hylton Conacher (ZR1HPC) <>:
2008/9/23 Carlos E. R. <>:
The backup has an advantage: you can recover from a software crash or finger error: the other disk is not mounted, so nothing is written to it "yet". On a raid, both copies would have the same wrong data.
The downside is that the machine is going to be a file/print/mail server and while I may have a backup as of yesterday, if I screw up a document, I cannot simply just restore the backup as other email would have been added to the live mail server that would be lost if it was restored from the offline backup. I guess the way around that is to have two rsync jobs being one for the mail directories and the other for only the document directories?
Or more frequent backups. Those are the cases where raid does not help: both copies of the document wold be broken. Restoring email queues is not so simple, anyway, maybe you could end resending mail already sent. I think that often it is better to leave the email as lost and resend from the client if needed. This is a situation for which RAID is better, IMO. A different thing would be a pop/imap server. - -- Cheers, Carlos E. R. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAkjY/7EACgkQtTMYHG2NR9V7FwCdHZOg9WYZ4tPPN1xmozVpaRla Y+AAniadGSruzhbxCfPq4/7NWBT3e8CF =Nm7d -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
2008/9/23 Carlos E. R.
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2008/9/23 Hylton Conacher (ZR1HPC) <>:
2008/9/23 Carlos E. R. <>:
The backup has an advantage: you can recover from a software crash or finger error: the other disk is not mounted, so nothing is written to it "yet". On a raid, both copies would have the same wrong data.
The downside is that the machine is going to be a file/print/mail server and while I may have a backup as of yesterday, if I screw up a document, I cannot simply just restore the backup as other email would have been added to the live mail server that would be lost if it was restored from the offline backup. I guess the way around that is to have two rsync jobs being one for the mail directories and the other for only the document directories?
Or more frequent backups. Those are the cases where raid does not help: both copies of the document wold be broken.
Restoring email queues is not so simple, anyway, maybe you could end resending mail already sent. I think that often it is better to leave the email as lost and resend from the client if needed. This is a situation for which RAID is better, IMO.
A different thing would be a pop/imap server. What would be different? I ask as it is actually a one person IMAP Dovecot, Postfix,SpamAssassin, Procamil mailserver store I aim to setup. The main purpose of the mail server is to lose as little email, if any email, at all. How can I ensure that no received mail since the last mirror/backup is not lost? Resending email already sent is fine, losing email already received is unacceptable as I will not know who to ask to resend?
Would running rsync continuously on the mail directories, and only at day end on the documents be possible? Regards Hylton -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 The Tuesday 2008-09-23 at 17:40 +0200, Hylton Conacher (ZR1HPC) wrote:
I guess the way around that is to have two rsync jobs being one for the mail directories and the other for only the document directories?
Or more frequent backups. Those are the cases where raid does not help: both copies of the document wold be broken.
Restoring email queues is not so simple, anyway, maybe you could end resending mail already sent. I think that often it is better to leave the email as lost and resend from the client if needed. This is a situation for which RAID is better, IMO.
A different thing would be a pop/imap server. What would be different?
A sending smtp server does not stores many emails, they are sent as soon as possible. There is almost no point in backup. A receiving server can store millions of emails.
I ask as it is actually a one person IMAP Dovecot, Postfix,SpamAssassin, Procamil mailserver store I aim to setup. The main purpose of the mail server is to lose as little email, if any email, at all. How can I ensure that no received mail since the last mirror/backup is not lost? Resending email already sent is fine, losing email already received is unacceptable as I will not know who to ask to resend?
Then the alternative is to store every email, as soon as it arrives, on two disks or servers. Notice that, as both are running continuosly, any of them could break as often as the other. - -- Cheers, Carlos E. R. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAkjZRRUACgkQtTMYHG2NR9VOuwCeKIBZ6QbjbBmLzcEsU5lEBp1C hBsAn0caC47vWvJor99jjEA/lTjQS6ez =Y3hE -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Carlos E. R. wrote:
The Tuesday 2008-09-23 at 17:40 +0200, Hylton Conacher (ZR1HPC) wrote:
I guess the way around that is to have two rsync jobs being one for the mail directories and the other for only the document directories?
Or more frequent backups. Those are the cases where raid does not help: both copies of the document wold be broken.
Restoring email queues is not so simple, anyway, maybe you could end resending mail already sent. I think that often it is better to leave the email as lost and resend from the client if needed. This is a situation for which RAID is better, IMO.
A different thing would be a pop/imap server. What would be different?
A sending smtp server does not stores many emails, they are sent as soon as possible. There is almost no point in backup.
A receiving server can store millions of emails.
I ask as it is actually a one person IMAP Dovecot, Postfix,SpamAssassin, Procamil mailserver store I aim to setup. The main purpose of the mail server is to lose as little email, if any email, at all. How can I ensure that no received mail since the last mirror/backup is not lost? Resending email already sent is fine, losing email already received is unacceptable as I will not know who to ask to resend?
Then the alternative is to store every email, as soon as it arrives, on two disks or servers. Notice that, as both are running continuosly, any of them could break as often as the other.
-- Cheers, Carlos E. R.
This is where procmail has it uses... a procmail recipe to forward incoming mail to a mail location or secondary mail server should have a good chance of duplicating the majority of incoming mail. However, it should also be noted *no* backup system will be guaranteed to be 100%, it is more of the decision of how close to that 100% one can reliably get. This is a basic cost benefit analysis, weighing the costs of the backup regime against costs of either loosing or recovering any damaged data, YMMV. (Using RAID in itself is *not* really a backup mechanism, it provides performance and continuity of service but that is a different issue). Email by its nature presents special problems, the dynamic nature of the data structure makes it highly probable that things will be missed during backup (unless you shutdown the mail system, backup the data and restart, data gaps are inevitable... and for most multi-user scenarios such a backup regime would be unacceptable and also probably impracticable). As any backup regime is only as good as its restore mechanism, and restoring email can be highly problematic, people can come to their own conclusions. BTW Anyone who claims that they have never lost data, is probably being rather naive. They have lost data but they just do not know it (yet), and if they did not know it they probably did not need it anyway :-) - -- ============================================================================== I have always wished that my computer would be as easy to use as my telephone. My wish has come true. I no longer know how to use my telephone. Bjarne Stroustrup ============================================================================== -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iEYEARECAAYFAkjZ84wACgkQasN0sSnLmgKxnACfZZVSkPugz+VKTM5I3qsK4ByL fXIAoOInR2VDsmaCwu6AVnm63MSOE9fX =UaE2 -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
The backup has an advantage: you can recover from a software crash or finger error: the other disk is not mounted, so nothing is written to it "yet". On a raid, both copies would have the same wrong data.
The downside is that the machine is going to be a file/print/mail server and while I may have a backup as of yesterday, if I screw up a document, I cannot simply just restore the backup as other email would have been added to the live mail server that would be lost if it was restored from the offline backup. I guess the way around that is to have two rsync jobs being one for the mail directories and the other for only the document directories?
If you screw up a document, restore the document. No one said you had to rsync the entire drive back. In this scenario, the backup is just a mounted filesystem like any other and you can copy individual files from it like any other directory. Or am I missing some implication of what you said? He did say one thing I guess which might have caused a confusion. When I do this kind of thing, the backup disk IS mounted all the time, it's just mounted as /backup or some other name that's out of the way of normal operations, not part of a raid array getting updated every instant. Or, if for some reason you want it to be unmounted normally, maybe so it spins down and suffers less wear or maybe so an ungraceful shutdown dosn't harm it, it's merely a "mount /backup" to mount it. I don't happen to think there is any reason to dismount between backups. If a power outtage happens, it will need to fsck during boot, but it will not actually find any bad data because the fs was idle and the kernel flushes disk buffers every N seconds (configurable). If the backup filesystem is reiser or ext3 with journelling, then the fsck will not even take long. I suppose unmounting could protect against more finger errors. Not impossible but less likely to erase anything on an unmounted disk. Then again the damned automounters that are on by default these days may place the backup disk helpfully on the users desktop and atomout in /media/* just like thumb drives and cameras, and so it's better to have it more statically configured and mounted after all. -- Brian K. White brian@aljex.com http://www.myspace.com/KEYofR +++++[>+++[>+++++>+++++++<<-]<-]>>+.>.+++++.+++++++.-.[>+<---]>++. filePro BBx Linux SCO FreeBSD #callahans Satriani Filk! -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
participants (4)
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Brian K. White
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Carlos E. R.
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G T Smith
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Hylton Conacher (ZR1HPC)