RAID Config question 1

[Jpmfresno]

Hello -
I have an IBM X345 server with 6 drives. Usually I setup the drives as follows: 2 mirrored for OS, 3 RAID5 for data and 1 Hotswap.

With this new server the drives are 143gb so there's alot of wasted space on the 2 mirrored.

I'm now considering setting it up as: 5 RAID5 and 1HS. Is there anything wrong with the OS on the HW RAID with the data? The drives are 143gb Ultra 320 and the RAID card is a 1channel U320. I'd of course still partition the OS and data (c: d out logically. I'd like some "best practices" on the RAID config.

The server runs Lotus Notes and we use about 200gb currently. Performance is important..any recommendations??

Thanks in advance,
Joe

 

[technome]

Two cents.....
Not sure if you have the same raid adapter, but IBM does use the same exact raid adapter as I have, OEMed from Lsilogic ..

Just spent about 7 days testing different array setups. One of the odd things I noticed is if you have a raid 5 and a raid1 setup on the same array adapter, the raid1 tests out poorly on ALL the following ..Intel's I/ometer, HDTACH, DISKBENCH, Sandra and Filecopy,( regretfully Winbench would not work on Windows 2003 Enterprise). All the benchmarks of the Raid 5 are so superior, especially the reads, to the Raid1, I would not place the OS, pagefile, log or temps on a separate raid 1, at least when the raid one is on the same raid adapter as the raid5. I need to get an Adaptec dual channel u320 scsi adapter, and test a raid1 setup on that, along with the raid 5 on the Lsilogic u320-2x, I would be surprised if this did not speed up a raid1 set. Another oddity, if a 2 gig group of files is copied from the raid 5 to the raid 1, as my array was setup, the benchmarks are poor, reverse the file copy from the raid1 to the raid 5, and there is a big improvement.. you would think raid 5 to raid 1 would be faster due to there being no parity creation involved.

Test machine..
Dual opteron 246 Iwill DK8n, Lsilogic u320-2x raid adapter, raid 5 with 5 or 6 Seagate 36 gig 15k drives, raid1 with 2 36gig Seagate 15k drives, writeback, read ahead enabled on the arrays, Os Win2003 Enterprise, 2 gig ram. Test partitions were 15 gig, and 50 gig, with 5 gigs of data on each (I refuse to test on bare drives). Fully patched, cleaned up, and defragged. Tweaks of the OS, had almost no affect, writeback is absolutely necessary on raid 5, readahead provided a 2-3% increase,

 

[alarnold]

I would not recommed running your OS off of a Raid5 array. While the RAID5 is great for files and programs, it will slow down your OS speed as it has to read information off or each and every drive of the array. The OS is always better off on a seperate drive or partition.
If you are concerened about wasted space, get a couple of smaller drives for the OS and the mirrored drive.

Al

 

[technome]

Alarnold...
Raid 5 has much faster read speed than raid 1. The writes are still faster with raid 5 with >4 drives, though slower than raid 10. Raid 1 sucks, perhaps with only a three disk raid5 array, raid1 would be faster, I do not know because I only create raid 5 arrays with a minimum of 4 disks.

"While the RAID5 is great for files and programs, it will slow down your OS speed as it has to read information off or each and every drive of the array."

Very true, but that is a benefit. The info is pulled off multiple drives at the same time thus increasing performance, reads do not require parity involvement unless the array is in degraded mode from a disk failure. Obviously you have not done extensive testing with raid1 and raid5, and have not had had servers side by side for comparison in production situations, I don't spread myths. Fully agree the Os and data should be in separate partitions, all may arrays are setup this way.

My testing has been done on multiple servers over the years, the newest on an lsi u320-2x, (8) 15k disks equipped server in multiple raid configurations.

 

[technome]

Correction for my previous post
" Very true, but that is a benefit."

Should read..
It can read info from each drive, but it does not necessarily have too if the data chunk is small,. If it is a large chunk, the data is read from multiple drives but that is a benefit.