Dell PowerVault 220S Руководство - Страница 32
Просмотреть онлайн или скачать pdf Руководство для Хранение Dell PowerVault 220S. Dell PowerVault 220S 44 страницы. Dell powervault 220s and 221s systems scsi drive enclosure
Также для Dell PowerVault 220S: Уведомление (28 страниц), Обновление микропрограммы (14 страниц), Руководство по эксплуатации (33 страниц)
Печатать страницу
A REFERENCE GUIDE FOR OPTIMIZING DELL™ SCSI SOLUTIONS
Data Protection Strategy
•
Battery back up: see "Write Cache policy considerations" section above.
•
Global hot spare
•
Dedicated hot spare
•
Consistency checks
PAGE 32
back up unit (see Table 5-2), there is a risk of data loss if system power
is lost while unwritten information is still in the cache.
Write Through
o
In write-through caching, a data transfer is completed when the disk
subsystem receives all of the data from the host. There is no risk of data
loss in a power-loss scenario (as in write back), but it is slower, since the
controller must wait for the hard drive to return a good status on the write
to the controller before proceeding to the next operation.
If the PERC controller has a battery backup unit (see Table 5-2) or if a
host system is powered by an alternate power source (e.g. UPS etc), the
controller's cache retains data during a power loss. Thus PERCs with
battery back-up not only provide the performance benefit of write-back
caching but also help ensure integrity of data during system power loss.
For data retention time please refer to Table 5-2.
A global hot spare can be used for any array that is on the same
o
controller as the hot spare.
More cost-effective than dedicated hot spares, but does not protect
o
multiple arrays as completely as dedicated hot spares.
A global hot spare is selected randomly and may be in a different
o
enclosure than the failed drive it is replacing. Can impact performance if
rebuilt array spans enclosures/channels.
A dedicated hot spare is assigned to one or more arrays.
o
Dedicated hot spares that reside in the same storage enclosure typically
o
have better performance than global hot spares.
Dell recommends using dedicated hot spares for critical data.
o
Consistency checks verify the correctness of redundant data in an array.
o
As during a rebuild, array performance will be degraded while check is
o
running.
Some PERC controllers allow pausing of consistency check and resume
o
it later or to resume the consistency check after the system reboots.
Recommended as part of regular system maintenance for critical data.
o
VER A02
11/17/2005