HP StorageWorks Scalable File Share - Manual (Page 93)

Creating a file system — EVA4000 storage 5–9
When quotas are enabled on a file system, the
itune
and
btune
settings (specified as a percentage) are
used in conjunction with the
iunit
and
bunit
settings to calculate the quantities of inodes and blocks that
will be reserved and released for a user or group.
If you decide to enable quotas on the file system, HP strongly recommends that you accept the default values
for the quota options. The default values are as follows:
•
iunit
:
5000
•
bunit
:
100
•
itune
:
50
•
btune
:
50
See Section 5.7 for more information on quotas.
5.1.4.1 OST Service ordering — EVA4000 storage
You must plan the order in which you specify the LUNs for the OST services to the
create filesystem
command carefully, because this eventually determines how files are striped across the OST services and
thus affects file system performance. The link between how OST services are specified to the
create
filesystem
command and file system performance is explained as follows:
• The order in which you specify the OST services to the
create filesystem
command is the order
in which the OST services are included into the logical object volume (LOV) that describes the file
system.
• The order in which the OST services are included into the LOV determines the adjacency of the OST
services.
• Files are striped across adjacent OST services.
When you are asked to specify the OST services, the
create filesystem
command lists the available
LUNs in the order that will achieve the recommended striping pattern.
Specify the OST services in such a way that LUNs that are on the same controller pair are adjacent in the
LOV. This ensures that I/O patterns through each controller are symmetric, because (in general) I/O from a
client node exercises both of the controllers in a controller pair simultaneously. This leads to more consistent
performance, because the aggregate performance through a controller pair is less than the sum of the
individual performances.
As an example, you can choose to create a striping pattern where all LUNs presented to the
a
controllers
are in sequence, followed by all LUNs presented to the
b
controllers. This pattern has the advantage of
providing higher performance if only the first 50% of the stripes are used; however, performance will be
lower if the second 50% of the stripes are also used, perhaps for a second application.
Note that if the correlation between the striping pattern (as determined by the specification of OST services
when the file system is created) and performance is not understood, performance figures may be
misleading.