HP Smart Array Controllers and basic RAID performance factors

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The IOPS that a drive can sustain influences the random read and write performance of drive arrays.
When using spinning media drives, the SAS-2 physical link’s bandwidth does not affect performance in application
environments that rely heavily on random read and write operations. Consider the following points:
• Currently, the fastest spinning media drives can deliver about 470 random IOPS using 4 KiB reads and writes. This
translates to a throughput of 1.8 MiB/s, which is less than one percent of a SAS channel’s bandwidth.
• Even in a larger RAID configuration using a SAS expander with six drives behind a single SAS channel, the aggregate
throughput is less than 15 MiB/s with six drives, which is still less than the SAS-2 physical link’s bandwidth.
• With Solid State Disks (SSDs) becoming universally available, IOPS levels have increased greatly. A 6 GiB SAS SSD can
deliver over 50,000 IOPS.
As Table 1 shows, no single drive can sustain a throughput that will saturate a 3 GiB/s SAS-2 physical link. With
sequential operations, particularly sequential reads, the SAS-2 physical link’s bandwidth can become a factor in overall
array performance.
Larger drive arrays can have multiple drives sharing the bandwidth of a single SAS channel. When more than two drives
share a single 3 GiB/s SAS channel, the performance for sequential operations will start to be limited by the bandwidth
of the SAS-2 physical link. With 6 GiB/s SAS drives attached to 6 GiB/s SAS-2 channels on the newer Smart Array
controllers, sequential performance should continue to scale until more than three drives are sharing each channel.
Table 1 lists typical performance numbers; other devices may have slight variations in performance.
Table 1. Maximum sustained throughput and random IOPS capabilities for HP HDD drives Sustained rate can be sensitive to the drive
model (even with the same rpm). For example, the newer 15K 6 GiB SSF drives support approximately 190 MiB/s.
Drive RPM Form Factor and Interface Maximum throughput
64 KiB sequential read
Queue depth > 4*
Typical IOPS
4 KB random read
Queue depth = 16
15,000 SFF 6 GiB/s SAS 195 MiB/s 385
10,000 SFF 6 GiB/s SAS 180 MiB/s 285
7,200 LFF 6 GiB/s SAS 150 MiB/s 135
7,200 SFF 6 GiB/s SAS 115 MiB/s 170
7,200 LFF 6 GiB/s SATA 150 MiB/s 135
7,200 SFF (3/6) GiB/s SATA 110 MiB/s 170
*These the numbers are for operations distributed randomly across the whole disk space.
Table 2. Typical performance capabilities for HP SSD drives.
Performance
class
Form Factor and
Interface
Random
reads*
Random
writes*
Sequential
reads
Sequential
writes
Enterprise
Performance SFF 6GiB/s SAS 40,000 IOPS 14,500 IOPS 415 MiB/s 180 MiB/s
Enterprise
Mainstream SFF 6GiB/s SAS 46,200 IOPS 9,800 IOPS 370 MiB/s 150 MiB/s
Enterprise
Mainstream SFF 3GiB/s SATA 32,000 IOPS 6,000 IOPS 257 MiB/s 129 MiB/s
*These numbers were Block size of 4096 bytes and queue of 16. The devices were tested at full capacity and preconditioned.