Dell PowerVault 221S (SCSI) - Manual (Page 34)

A REFERENCE GUIDE FOR OPTIMIZING DELL™ SCSI SOLUTIONS VER A02
PAGE 34 11/17/2005
drives supported by the PV22xS). Mixing spindle speeds within the same
array will impact array performance, especially in a striped (RAID0, RAID10
or RAID50) environment. Higher RPM drives will have to wait for the slower
ones to complete the operations. This is the case regardless of cache policy
settings.
Interface Channel Options – Internal/External/Multi channel device configuration
• See Table 5-2 for internal/external connector details for each controller.
• Do not connect devices both internally and externally on any one channel.
• Termination
o The PV22xS is also already terminated. No external SCSI bus
terminators are needed when connecting to a PV22xS.
• Spanning of Arrays
Dell’s PERC controllers provide additional array configuration options of
spanning logical arrays. Dell supports spanning of logical arrays only across
multiple channels on same PERC controllers. If multiple PV22xS are
configured (Joined or Split topology - Figure 4-3a) on the same PERC then a
logical array may be spanned across multiple PV22xS.
In general, spanning of logical arrays across multiple channels on a controller
improves data throughput. With the introduction of another data path,
depending on the RAID level, the configuration may compromise data
availability. When configuring logical arrays across multiple channels it is
essential to understand the trade-off between performance, reliability and
availability of data. Depending on the RAID level for an array, spanning may
offer a better solution than without spanning. The following table lists pros
and cons of spanning in relation to RAID levels: