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Chapter 5 Configuring the xStack Storage Array

Table 5-13 Modify System TCP/IP Settings Dialog Box Settings

Setting

Description

Max Segment Size

Indicates the maximum size TCP segment that can be accepted on a TCP/IP
connection when the connection is established.

Window Scale

Lets you use large windows during TCP/IP connections. On fast, high-bandwidth
networks, a large TCP window provides greater efficiency by allowing for a greater
amount of unacknowledged data.

TCP Timestamp Enabled

Causes the receiving computer to send a time-stamp reply back to the originating
computer. Systems can use time-stamp requests and replies to measure the
transmission speed of datagrams on a network.

Time to Live (TTL)

Specifies the default time to live (TTL) value for IP packets generated by the Windows
TCP/IP stack.

PMTU Enabled

Lets the xStack Storage Array automatically adapt its packet size. Disabling this option
forces the system to keep its default packet size (576 bytes), even when it receives an
ICMP request to change its packet size; this can render some remote systems
unreachable, because if intermediate systems on the path to the remote system cannot
support the default packet size, the xStack Storage Array ignores their requests to make
the packets smaller.

Upper Layer Count Reset

Resets the TCP/IP upper layer counters. Resetting the counters simplifies the ability to
look at the counters for an accurate percentage of packets sent or received.

5.4.11

Setting the Spare Count

A spare is a drive that is present in the system (in the

Available Pool

) that cannot be used for

any reason, except to rebuild space used by a volume on a failed drive. If a drive fails, the xStack
Storage Array tries to find a replacement extent for every extent on that failed drive that was
part of a redundant volume. First, a replacement extent is sought on a drive in the volume’s pool
(currently, the

Blade A Base Pool

). If space is not found in that pool and a drive exists in the

Available Pool

, one drive is obtained from the

Available

Pool

and an extent is selected from that

drive. In either case, a rebuild task starts to rebuild the volume’s extent. If the available pool is
empty, some volumes may not be rebuilt. The spare count exists to reduce that likelihood.

The spare count default is 0, which means that no drives are kept in reserve for use in rebuilding
extents (i.e., all drives can be obtained from the

Available Pool

for any purpose). Automatic

Volume Creation, for example, takes drives from the

Available Pool

automatically as needed to

satisfy the parameters in the request. If the spare count is set to a non-zero value, that number
of drives is retained in the

Available Pool

for use only for rebuilds (i.e., operations other than

rebuild cannot take a drive from the

Available Pool

if taking that drive results in the

Available

Pool

having fewer drives than the spare count value). For example, assume that the spare count

is one in an enclosure with 12 drives installed. If the administrator tried to perform an Automatic
Volume Creation with both sliders at 10 (their maximum values), the volume is created using 11
drives, without touching the twelfth. If a drive fails, the twelfth drive moves automatically from
the

Available Pool

to the volume’s pool, so its space can be used to rebuild the original failed

extent.

Click the

xStack Storage

icon on the

Physical Resources

tab.

Perform one of the following steps:

–

On the

File