DataDirect Networks S2A9550, Руководство пользователя

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D a t a D i r e c t N e t w o r k s S 2 A 9 5 5 0 U s e r G u i d e
M a n a g i n g t h e S 2 A 9 5 5 0
3.2.11.1 Non-Cache Coherent
In this configuration, the couplet S2A9550 communication occurs over the internal UART. Each
S2A9550 owns LUNs and tiers. Spare drives are owned by individual S2A9550 units, according to tier
ownership.
In healthy situations, the S2A9550 cannot access LUNs or tiers owned by the other S2A9550.
However, if the other S2A9550 is failed, the healthy S2A9550 will have access to all LUNs and tiers.
Users, via mapping, can be assigned any combination of LUNs. In a healthy environment, the users
will only see LUNs owned by the S2A9550 to which they are connected.
For example, a user is given access to internal LUNs 5, 6, and 7, which are mapped to external
LUNs 0, 1, and 2 respectively. S2A9550 1 owns LUNs 0 and 1 while S2A9550 2 owns LUN 2. The user
is physically connected to S2A9550 1, thus, it will only see LUNs 0 and 1. The user will not be able to
access LUN 2. If the user was physically connected to S2A9550 2, the reverse would be true, only
LUN 2 would be accessible. When an S2A9550 fails, the user will be given access to all mapped LUNs
regardless of the physical connection.
Data cache is not copied from one S2A9550 to another. If a S2A9550 fails, all “dirty” data in cache
will be lost. Thus if data integrity is paramount, writeback cache should be disabled.
3.2.11.2 Cache Coherent
In this configuration, each S2A9550 only owns tiers. This is only for disk failures and rebuilds. Spare
drives are owned by individual S2A9550s, according to tier ownership.
Each S2A9550 can access all LUNs. Each user, regardless of physical connection, can see all mapped
LUNs.
The couplet S2A9550 communication occurs over the internal UART and external Ethernet. If the
S2A9550s detect an Ethernet failure, S2A9550 2 will be failed. (This means that an external event can
cause an S2A9550 to fail even though the S2A9550 may be perfectly fine.) Therefore, it is highly
recommended the S2A9550 Ethernet resides on a private Ethernet segment.
Data cache is not copied from one S2A9550 to another. If a S2A9550 fails, all “dirty” data in cache
will be lost. Thus if data integrity is paramount, writeback cache should be disabled.
To enable/disable the cache coherency function, type: DUAL COHERENCY=ON|OFF
<Enter>.
Default
is dual coherency disabled which is the non-cache coherent configuration.
The DUAL TIMEOUT=X command allows you to set the cache coherency timeout for cache node
requests in seconds. Valid range is 0 to 255 seconds. Default is 2 seconds. The timeout value should
be less than the host timeout value (
HOST TIMEOUT=X ). A timeout value of 0 allows for only one
retry.
NOTE : In dual mode, LUNs will be “owned” by the S2A9550 unit via which they are created. Hosts will
only see the LUNs on the S2A9550 that they are connected to, unless cache coherency is enabled.
3.2.11.3 Fail / Restore the Other
S
2
A 9550
Unit in the Couplet Pair
To fail the other S2A9550 unit in the system to perform maintenance, type:
DUAL FAIL
<Enter>
The healthy S2A9550 unit will take ownership of all the LUNs/tiers from the failed S2A9550 unit.
To restore the other S2A9550 unit in the system to healthy status after failure recovery, type:
DUAL HEAL
<Enter>
Ownership of LUNs/tiers are transferred back to the S2A9550 unit.