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What is the best array for installing server OS or DATA partition, RAID 1 or RAID 5?


My question is as follows. Is there a "better" choice for installing the server OS? I know some people recommend installing the SERVER OS in a RAID 1 DISK and the data in a different RAID 1 or a RAID 5 array. But is it just as well if you simply create a single RAID 5 array and install OS and DATA there (in different partitions though...)

I would like to know what is the general consensus for different types of server installations...

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seperate raids will give better performance than seperate drives on the one raid.
consider a raid as one drive - it isnt ideal to put the two partitions on the one drive.

then the type of raid for each drive will depend on the application but this is what I like..

OS - 2 drives - Raid1
Data - 4 drives - raid 10
Other- 2drives raid1 - or one drive - on here I put the data that either I never want to back up or stuff that is irrelevant to backup. Such as antivirus, and WSUS, and some temp work space.
As I use an imaging product for backup (storage craft) and backup changes every 15min this keeps data that changes often on a different drive and makes my incremental backups smaller/more relevant
"Best" is relative, so I'll make this rather generic for typical office database general purpose server running Win2K8, or any *NIX

Go RAID1 for the O/S, using either a quality controller with battery backup, or host-based RAID.  With either, you get read load balancing, so in perfect world read performance is 2X that of a single drive.  Write performance is close to the same as if you had a single drive.

There is NO significant CPU overhead if you do any type of software RAID. RAID calculations are done in microseconds and nanoseconds.

RAID5 is great for high throughput read, but bad to worse in random and sequential I/O.  RAID5 is much worse when you are degraded and have to rebuild.  I've seen it take over a week in some cases.

Personally, one should never do RAID5 anymore.  I recommend RAID1 for O/S, swap, scratch index/tables, and journals.  Then use RAID6 for data.  That way you are protected against data loss in event of a multiple drive failure.

Also consider a pair of small SSDs with host-based RAID on your SATA ports.  $1000 will get you almost 50,000+ random I/Os per second, all 100% protected.

If you're talking a 10-200+ Terabyte server then I would recommend some tweaks and get into these items in depth, but that depends on a lot more variables about intended use.
of course if you are looking for capacity& redundancy for the best $ then one raid 5 array - but it wont give the best performance for your $
profanostraAuthor Commented:
Wow, excellent viewpoints and suggestions! Thank you very much for your comments gentlemen.
Have a good weekend.
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