RAID 5 performance

[bdollar]

Part 1:
did some searches on here but couldn't find anything. my question is regarding raid 5 performance. both reads and writes. If i have a decent raid controller and i have 1 or 2 extra drives (so 4 or 5 total). How is the RAID 5 read and write performance compared to a single drive of the same type?

Part 2:

How much REAL improvement do you get in reads and writes on RAID 0 vs. single drive. I know it is no redundancy and all that jazz. but just curious what gains you get.

If it matters both of these questions may ultimately pertain to 15k scsi drives but would like to know if it is a different answer on a typically 7200 rpm sata drive.

Thanks!!

 

[rozar]

RAID 5 reads are good due to spindle count and stripping but access times will fall and writes do slow down because of parity being written. Plus if you use a large stripe size and write files to it smaller than that size it is really slow.

RAID 0 depends so much on the application if its just really big files coming out of a scratch space for instance and its a good hardware controller it will fly. If its an onboard (even scsi) controller and its the OS and RAID 0 then its pretty ugly. Access time takes a hit and it may not be worth it, 1 drive may be faster.

Then there is the question of the controller, a really good controller can make a big difference.

If you are talking 15k drives and you dont have them yet by all means get SAS and not SCSI.

If this is a server a typical setup is 2 really fast drives in RAID 1 for OS/apps and RAID 5 for data, these can even be SATA (or the new 7200 rpm SAS). When you use multiples of 7200 rpm SATA drives the spindle speed can get pretty high and the cost per GB stays at a decent level compared to 15k SAS.

 

[bdollar]

so for best possible performance with redundancy is it still 5? I was under the impression that was better than 1+0 or 0+1. and recovery time if one fails (like RAID 6) isn't a concern.

 

[bdollar]

so i'll elaborate. long story so try to keep it short. i may be getting 4 300 gb cheetahs. not costing me anything. probably going to build a rig around them. might as well use them. i know I could sell some and be as good off but i'm not going to so just want to talk about uses. Wouldn't mind some redundancy just to not have to hassel if a drive dies but it isn't an absolute must. way I look at it i can :

1. 4 drives RAID 0 no redundancy
2. 4 drive RAID 5 redundancy but maybe a hit in performance.
3. 2 drives for OS and gaming and 2 drives in a raid 1 for redundancy of things i want to save and aren't as concerned about speed with.

I can spend a chunk of $$ on a controller if it will make a big differece. considering the value of the drives I have no problem with that.

my 1st goal is to have it functioning fast as I can (i know I know it will be fast regardless). 2nd goal is redundancy if I don't have to sacrifice too much speed.

Typical use: gaming 1st. photo editing and video editing second. and if it matters you can assume the other components will be good. sorry if this is a total noob post. haven't dealt with RAID and haven't dealt with this many HDDs before.

 

[rozar]

Well first I would want to ask what kind of cheetahs? This matters alot because some 15k drive are actually pretty slow. Some fall into the 80mb a second catagory. Is this SATA or SAS? This would be a factor in making a choice of buying an expensive controller or not.

Then talking RAID levels

RAID 0 fast, no overhead, no redundancy, slower access time
RAID 1 x2 decent reads and writes, reduncancy, bad overhead loss of 2 drives
RAID 5 good spindle speed, slower access, redundancy, slow writes
RAID 10 bad overhead, good speed for reads and writes, redundancy
Single Drive & RAID 5 good reads and writes for the OS, good speed for data, redundancy for data, good access for OS,


Of those in "this situation" (all 4 drives are the same size and speed) I like RAID 10 as long as you dont mind the overhead. You can even partition the volume to make a small partition for OS and apps and then leave a larger portion for data.

If this is older SAS or even SCSI drives I might even sell the drives if I were you. It woudl not be worth it to buy an expensive controller for those types of drives.

 

[bdollar]

SEAGATE, 300GB Cheetah 15K.5, SAS 3gb/s, 15K RPM, 16MB Cache, 3.5-Inch

Random read seek 3.5msec Write 4.0msec

I think it is pretty good and not the old, slower ones but is there any more scoop you would need to tell?

Overhead is fine. getting the space of 2 is still 600gb. that is a lot of space.

 

[rozar]

Those are good drives for sure. I would not mind either single drive and RAID 5 combination or RAID 10 for this. With RAID 10 you can get a cheaper controller too.

Look at the Adaptec 5 series or 2 series controllers

Link for 2 series

http://www.adaptec.com/en-US/products/Controllers/Hardware/sas/entry/SAS-2405/

As long as you have air flow around the controller it is a solid choice. The 3ware is also a good one. If you do not have a backplane you will need a "special" cable to connect to the drives.

See this post
http://www.tomshardware.com/forum/forum2.php?config=tomshardwareus.inc&cat=32&post=246509&page=1&p=1&sondage=0&owntopic=1&trash=0&trash_post=0&print=0&numreponse=0&quote_only=0&new=0&nojs=0

 

[rozar]

By the way that is the same SAS drive I have. I also have 4 of them but I didnt put them all in 1 system. I have them in 3 systems.

 

[bdollar]

yeah i'll have to think about it. thanks for some great info. i may calm down a little and spread the wealth into more than one. but this gives me some options. thanks!

 

[xxsk8er101xx]

yeah i'll have to think about it. thanks for some great info. i may calm down a little and spread the wealth into more than one. but this gives me some options. thanks!

Those are some impressive drives i'm jealous heh.

Another good controller brand name is LSI. I like Adaptec also.

Just for the love of god don't buy a pci card! I hope you have at least a pci-x slot or a pci-e 4x slot.

Anything else for RAID is pointless.