Configuring The Md3000/Md3000I; Determining The Best Raid Level - Dell PowerVault MD3000i Tuning Manual

Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices
• Profile of mean I/O direction; this is usually the ratio of Reads to Writes

4 Configuring the MD3000/MD3000i

There are two ways to configure the MD3000 and MD3000i storage systems.
The most common and easiest method is using the MDSM. The MDSM allows
automatic configuration settings that provide reasonable configurations with little
knowledge of performance tuning required.
A manual configuration option is also available using the command line interface
(CLI), providing more flexibility but requiring more knowledge of performance
requirements.
For a link to the MDSM and CLI guides, see Appendix C: References.

4.1 Determining the Best Raid Level

The first step involved in tuning an MD3000 or MD3000i external storage array is
to determine the RAID level most appropriate for the solutions given the
application. In the proceeding document, please note that RAID 0 is excluded
from most information in this paper due to the lack of data protection. This does
not mean the use of RAID 0 is undesired, just that it should only be used for non-
critical data. In general, RAID 0 generally provides better performance than RAID
1/10, 5 or 6. Additionally, RAID 6 is not always referenced specifically; most
comments applicable to tuning RAID 5 are directly applicable to RAID 6 unless
otherwise noted. In situations where the increased fault tolerance provided by
RAID 6 are desired, please note that a performance penalty is observed when
compared directly to RAID 5 due to the additional parity calculation and the extra
physical disk required for implementation.
An important consideration when determining the appropriate RAID level is the
physical disk cost required by a RAID level. Physical disk cost, is the number of
physical drives worth of capacity that are sacrificed to provided the desired data
integrity level. The physical disk cost of each RAID level is different, and may
impact the decision for which RAID level is most appropriate for a chosen
environment. RAID 0, having no level of redundancy has a physical disk cost of
zero. RAID 1/10 has the highest disk-cost in disk groups containing more than 2
drives. Half of the physical drives in a RAID 1/10 are always consumed for the
mirror. RAID 5 has a fixed 1-physical disk per disk-group cost, i.e. with a RAID 5
set of n disks, only n-1 worth of capacity is available. Similarly, RAID 6 has a
fixed two physical disks per disk-group cost, or n-2. In RAID 5 and 6, these extra
drives account for the space required to maintain the levels of parity information
for each stripe.
December 2008 – Revision A01 Page 6