Developers Guide

18 Understanding RAID with Dell SC Series Storage | 3104-CD-DS
Figure 7 indicates the operational advantage during writes that RAID 10 has over RAID 5. In a single
redundant tier, all application updates go to RAID 10 with only two I/Os, in contrast to the four I/Os needed for
an application writing to RAID 5.
Difference in write penalty between RAID 10 and RAID 5
For most SC Series arrays, Tier 1 has RAID 10. However, if the tier requires dual redundancy writes, they
occur on RAID 10-DM. Table 5 shows the Tier 1 and RAID-level write penalties and where application writes
occur according to the redundancy setting.
Tier 1 application RAID level write policy based on redundancy
Redundancy
RAID level
Write penalty
Application writes
Single
RAID 10
2
Yes
Single
RAID 5
4
No
Dual
RAID 10-DM
3
Yes
Dual
RAID 6
6
No
Note: SC Series arrays follow this policy as long as appropriate space is available for each RAID level and
tier.