RAID 1 vs RAID 5, which one is fast in performance?

Last Post 04 Mar 2003 09:25 PM by bigelectricmac. 7 Replies.
AddThis - Bookmarking and Sharing Button Printer Friendly
  •  
  •  
  •  
  •  
  •  
Sort:
PrevPrev NextNext
You are not authorized to post a reply.
Author Messages
Huifong
New Member
New Member

--
21 Apr 2002 03:08 PM
I have a general question for Raid 1 vs Raid 5 for a log file.

Say Raid 1 has one pair of mirrored disk controllers while Raid 5 has three disk controllers. Which one is fast in performance generally?
satya
New Member
New Member

--
22 Apr 2002 12:08 AM
It depends on number of factors to consider which ones has better performance :

Basically hardware based RAID 5 has an excellent performance and does not compete for processor cycles. Its expensive compared to the others

RAID 1 also has an excellent redundancy and similar to above, as far as cost is concerned its more than RAID 5.

Whereas, windows NT-based RAID 1 has good redundancy, low cost. But little hassle is uses system processing resources.

Above all windows NT based RAID 5 has excellent performance and low cost.

HTH
Huifong
New Member
New Member

--
30 Apr 2002 03:18 PM
Thank you all kindly for your replying.

Here is my understanding of the mechanism of hardware RAIDs.

RAID 1 (one pair of mirrored disk controllers):

Writing - RAID 1 needs one record writing time for a record because two disk controllers can write simultaneously;

Reading - RAID 1 only needs half time to read a record because two controllers can retrieve the same record simultaneously from two mirrored disks.

RAID 5 (three disks controllers):

Writing - a record is spread into to two disks and then the calculated parity is written to the third one. What I'm not sure is whether those writings happen simultaneiously or one disk after another? If it's former, then RAID 5 is faster in writing than RAID 1 (more disk controllers a RAID 5 has, more faster it is). But if it's the later case, then RAID 5 is slower than RAID1 as it needs one record writing time plus the parity calculation and writing. Please let me know which one is the case!!!

Reading - RAID 5 reading is faster as all the disks can retrieve the same record simultaneously except the one for parity. And more disks it has, more faster it is in reading. So RAID 5 is faster in reading than RAID 1.

Cost & log file size are not concerned, log reading time is not an issue here either as we don't use log back up.

The decision to use RAID 1 or RAID 5 for a log file I think will depend on RIAD 5 writing time. Am I right?

Cheers
Huifong
satya
New Member
New Member

--
02 May 2002 12:07 AM
Earlier we had DB files on RAID5 and kept on RAID 10 for a better performance, but nothing much to see the result. So reverted to RAID5 which gives OK results and translog on RAID 10 is good idea.
Rah
New Member
New Member

--
07 May 2002 08:07 AM
I concur with what most people have written here and would suggest putting log files on a raid 1 (The transaction log file is written serially; therefore, using a separate, dedicated disk allows the disk heads to stay in place for the next write operation.) As well as using a RAID 5 for data since it provides redundancy of all data on the array, allowing a single disk to fail and be replaced, and in most cases without system downtime. You must consider system downtime as a factor when calculating your overall system speed. Data striping (RAID 0) is the RAID configuration with the highest performance.

If you need more explanation, try looking at SQLBOL. In particular, try these for topics:
RAID Levels and SQL Server
RAID

HTH - Rah
prospec
New Member
New Member

--
03 Mar 2003 11:30 AM
what if the database is marked for replication? what raid set would you want then?
mimadon
New Member
New Member

--
03 Mar 2003 01:34 PM
Just a word of caution regarding OS software-based RAID (either RAID 1 or RAID 5):

As Satya notes, using OS-based mirroring or striping is a low cost solution. However, you get what you pay for.

If you really need to protect your data, you should consider hardware-based RAID solutions. Battery-backed, intelligent disk controllers may be more expensive up front, but that price will look small the first time your OS-based solution hiccups and corrupts your OS RAIDed mirrors/arrays.

I offer this advise based on painful, personal experience.
bigelectricmac
New Member
New Member

--
04 Mar 2003 09:25 PM
Very timely topic, since we are looking to buy an application server for an implementation of SQL Server 2000 Standard.

From th book SQL Server 2000 DBA Survival Guide, the author suggests the following:

o RAID 1 for transaction logs.
o RAID 5 for systems with frequent reads.
o RAID 10 for systems with frequent writes.

At least that is the experience of the author.
You are not authorized to post a reply.

Acceptable Use Policy