Re: RAIDING different size drives
- From: David Brown <david@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 12 Jun 2009 09:09:04 +0200
Arno wrote:
David Brown <david@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:<snip>Rod Speed wrote:David Brown wroteSydney Lambe wrote
Of course, the idea of software RAID on windows to improveWrong.
reliability is an oxymoron.
It would have been more accurate of me to say "on a windows desktop".
This is perhaps not the group for discussing OS reliability, but from my own experience (running IT for a small company for many years) and from endless accounts on the web, windows is generally an inferior choice of OS for solid and reliable storage. Factors that improve the reliability (regardless of the OS) are better hardware (desktops are typically fast but poorer reliability), server usage rather than desktop usage (fewer programs, with more limited scope and more testing), higher security (avoiding malware or attacks), and better environment (such as UPS for power, cooled server room, no spilled coffee, etc.)
Interestingly my current employer uses Linux software RAID for
the base system and then puts Windows installations in VMWare
on top of that. This works pretty well, but requires people that
understand Linux and Windows.
It requires IT administrators that understand both Linux and Windows (and these days, most IT departments of any size should understand both). Users, for the most part, should be kept blissfully ignorant of which machines are "real", and which are "virtual", and what OS they are running.
You don't store files on a windows desktop and expect it to be "reliable". You store your important files on a server (preferably on a non-Windows system). You keep good backups, whether you have a server or not. If all you have is a windows desktop with typical usage patterns, then using raid, especially windows software raid, is a such minor step towards reliability that it's not worth considering until you've looked at the system as a whole. An external harddisk which you plug in, take backups, and unplug on a regular basis would do far more to protect the safety of the data files than mirroring the internal hard disk.
I agree. There is a cultural difference. Unix folks expect their
stuff to reside on servers, be backed up by the system administrator,
etc.. If they operate their own (say) Linux box, they do all that
by themselves, because they regard it as part of professional
computing. The MS crowd comes out of the "computing is easy"
crows that then sometimes becomes the "where has all my data
gone" crowd.
But even the more knowledgeable MS users tend to use servers with system administrators today.
I think in most companies, most data is held on centralised servers even if the network is entirely Windows based - although there's always some users that save things under "My Documents", or use POP3 email. IT administrators don't like it when users do that - because they get the job of finding the lost data again.
For smaller companies and home networks, then I agree there is a definite cultural difference. People use old PC's running Linux as home servers for their email and files - very few think of buying and installing a Windows server.
Use RAID on a windows machine to improve speed, but if your data isOr use mirroring to improve the reliability.
important then save it regularly on a reliable system.
File system corruption, due to Windows itself or to malware runningWrong.
on the system, far outweighs the risk of hardware disk failures
I've seen a fair number of computers through the years, and I have very seldom seen physical hard disk failures. I *have* seen plenty of corrupted disks, and I have helped out people with malware on many occasions. Mirroring just means you have two copies of the corrupted file systems.
I habve seen a number of disk failures. I have run about 50 drives
in a climate controlled server room for 4 years, with maybe one
unexplained failure (the others were dropped in shipping). I have
seen a RAID1 of Maxtors fail from heat (helped the colleguae that
set this up to recover some data). I have seen a lot of DeathStars die, including 2/2 of my own. I also have one 2.5"
HDD in a RAID1 that has a tendency to transient errors. It drops out of the RAID about 2-3 times a year.
Part of the difference is luck (I've not used DeathStars), but it's mostly a matter of numbers - there are maybe 10 drives in the various servers in our server room, and my guess is that they are much less used than the ones in your server setup.
I agree that for well handled disks under good operating
conditions fail rarely, and in line with the manufacturer-stated
reliability. However many desktop systems do not provide
these conditions. And there can be surprises, like the DeathStars
or the exceedingly heat-sensitive Maxtors of some years ago.
Yes, that's another reason why a typical server is more reliable than a typical desktop machine.
I should of course have mentioned the biggest cause of data loss - user error. Again, mirroring is useless against this, while a good backup regime gives protection.
Agreed. And it helps to use version control systems and rotating
or incremental automatic backups to other systems.
(though corruption may affect only some files, while hardwareMangled all over again.
failure can affect the whole disk).
And when Windows or malware mucks up your file system, your RAID 1Just as true of any other OS.
setup ensures that the same errors are copied over to the mirrored
drive.
Absolutely - and other OS's are not immune to either malware, attacks, or file system corruption. But they are (assuming they are configured and administered properly) orders of magnitude lower risk. The same applies to server usage rather than desktop usage, regardless of OS - it hugely lowers your risks of malware or corruption.
Indeed. Wirh a Unix/Linys system, you need to be scared maybe a year or so. With Windows, you need to be scared half of the time.
In short, RAID can improve speed and/or uptime, but it does notWrong.
noticeably improve data security,
and it is not a substitute for backups.But does give added protection against the failure of a drive.
Yes, but hardware failure is such a tiny risk compared to everything else, that it's not worth bothering about until everything else is in place.
I do not agree. RAID1 is cheap, especially as software RAID.
RAID on a server is cheap, and worth the cost. RAID on a desktop is money wasted (unless you are looking for speed gains), since the same money could probably be better spent in other ways for greater reliability.
If you have two hard disks in a desktop machine and you want to improve reliability for your data files, you format the second disk as a separate partition labelled "backups". You take regular copies of your data files from your working disks into separate directories on the backup disk (there are many ways to organise this, but that's a topic for another thread). This protects against user error, against most corruption (you are unlikely to corrupt the two independent file systems), and gives reasonable protection against hardware failure (if your main drive dies, you'll have to re-install your OS and software on a new disk, but your data is safe).
Well, this is one approach. What I do is have RAID and do copies to
other partitions. Except for Windows, there I just have backup.
Another thing to consider is your access to the files in the case of operating system death, which is not exactly uncommon on desktop windows systems. In such cases, your data is safe on the disk, but the windows registry or critical files are corrupted. Windows will do this on its own occasionally, especially if provoked (such as by power failures), and third-party "security" software updates are notorious for rendering windows unbootable. And of course, malware of all sorts can similarly render the machine useless.
One of the reasons I regard Windows as a "toy". Wit Linux/FreeBSD/...
I can just backup/move/restore an application directory and things will work. No single-point-of-failure monstrosity like
the registry. But there is well-programmed Windows software that
does not need/use the registry. For example, you can copy the World of Warcraft installation directory to an entirely different machine and it works there too. Unfortunatrly, not many of the software
defelopers on the MS platform "get it". One of the cultural
disadvantages.
How do you then get your data files off the broken system, before trying to fix it or to use a "system restore" CD that deletes all your data?
These are a cruel joke IMO!
Ideally, you use the copies that are on a server, or your backup copies. If you've got a second copy on an independent hard disk, you can use that disk in another machine, or remove it until you've fixed the main drive. You can also use a live Linux CD and access the files that way. But if everything is on a raid setup, you don't have an independent way to access the data. Maybe a live Linux CD will be able to access the data, maybe not.
If it is a Linux software RAID, it will. Otherwise dm-raid may help.
But you absolutely need to test this before you have a problem.
This is definitely one of the big advantages of using Linux software RAID over any other kind of RAID - recoverability if things go badly wrong.
.
- References:
- RAIDING different size drives
- From: Sydney Lambe
- Re: RAIDING different size drives
- From: David Brown
- Re: RAIDING different size drives
- From: Rod Speed
- Re: RAIDING different size drives
- From: David Brown
- Re: RAIDING different size drives
- From: Arno
- RAIDING different size drives
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