PowerMax and VMAX All Flash Solutions Design (TimeFinder SnapVX Concepts and Operations) Flashcards
What is TimeFinder SnapVX?
mechanism for efficient snapshots without the need for target devices
When are target devices required in TimeFinder SnapVX?
only for presenting the snap to another host
How many target volumes can be linked per source volume in TimeFinder SnapVX?
1024
What does a write to a source volume require?
one snapshot delta to preserve the original data for multiple snaps
What happens if a source track is shared with one or more targets?
write to this track preserves the original data as the snap delta
delta shared to all targets
How many snaps per source volume on TimeFinder SnapVX?
up to 256 snaps per source volume
What is a Linked Target Volume?
device that is linked to SnapVX snapshot to make the snap accessible to the host
What are the two modes that Linked Target Volumes can have?
nocopy mode
copy mode
What is NoCopy mode for linked target volumes?
does not copy data to the linked target volume but still makes snaps accessible using pointers
snap will not be available after the target is unlinked since target data may no longer be associated w/ snap
What is Copy mode for linked target volumes?
copies of all relevant tracks from the snaps to the linked target volume to create a complete copy of the snap
copy remains available after the target is unlinked
What is a snapshot?
point in time copy of a source volume
uses pointers in cache to indicate which version of a track is applicable to the specific snap
either a track that resides on the source volume or snapshot delta
What is a snapshot delta?
point in time version of a source volume track that was preserved during a host write to a source volume that had an active snap
What is a source volume?
device that has SnapVX snapshots from it either with or without linked targets
What is a storage resource pool (SRP)?
collection of data pools which provides physical storage for TDEVs
managed by FAST
What is the default technology for SnapFinderVX snapshots?
redirect on write
What is the alternative technology for SnapFinderVX snapshots?
asynchronous copy on first write (ACOFW)
When would it be best to use ACOFW vs ROW snapshots?
to prevent source data from being redirected to a less than ideal performance or compression tier
What are Snapshot Generations on PowerMax?
each snapshot is assigned a generation number
if the name assigned to the snapshot is reused then the generation numbers are incremented (starts at 0)
if each snapshot has a unique name they are all generation 0
What happens if you terminate a snapshot on PowerMax in relation to generations?
results in reassignment of generation numbers
How long are snapshots retained on PowerMax?
kept until terminated or time-to-live (TTL) is set
What is a TTL?
used to automatically terminate a snapshot at a set time
can be specified at time of snapshot creation or made later
What happens if a snapshot has a TTL but also has linked targets?
it isn’t terminated
terminated only when the last target is unlinked
What are secure snapshots?
prevent admins from intentionally or unintentionally deleting snapshot data
What happens when creating a secure snapshots?
you assign it an expiration date or time either as a delta from the current date
once snap expiration date passes and no links have been established PowerMax OS automatically deletes the snap
What is the relation between creating secure and normal snaps?
a snapshot can be converted to a secure snapshot but a secure snap can’t be converted to a normal snap
What happens if a secure snapshot hits the expiration date but it has linked targets?
snapshot isn’t deleted but it’s no longer considered secure
What is reserved capacity?
ensures that their is sufficient capacity available in the SRP to accommodate new host writes
percentage of the SRP that can be only allocated to new host writes
What happens when allocated capacity reaches the point where only reserved capacity remains?
a snapshot fails at the next attempt to create a new snapshot delta
snapshot has to be terminated
copy to targets halt and cannot be completed
copy resumes if free space is made available in the SRP or if the reserved capacity is lowered
What are replication data pointers (RDP)?
keep track of snapshot deltas in SRP
portion of metadata dedicated to these operations
What is the metadata that holds RDPs called?
Replication Cache
if exhausted snaps can begin to fail
When is Replication Cache used?
by SnapVX snaps and VP Snap sessions
replication cache increases as SnapVX and VP Snap source devices are written to - since there are more PIT data to manage
What doesn’t affect replication cache usage?
SnapVX Linked Targets
clone sessions
mirror sessions
What happens to replication cache usage after a snap deletion?
not immediately made available again for use
process can take some time since it’s designed as a background process to not interfere with primary performance operations
What is important to know before creating new snaps?
current Replication Cache usage should be checked before creating new snaps immediately after deletion
What is the different between VMAX and PowerMax for Replication Cache?
all systems follow the same algorithm to determine percentage of metadata to allocate to replication cache
high snapshot environments can get RMA to get a new algorithm for build
What must occur for a snapshot to provide access to PIT data to a host?
snap has to be linked to a target volume
can be in copy or no copy mode or both
What is the default mode for linked target volumes?
no copy
What happens if you write to a linked target?
does not affect the snapshot
target can be relinked to the snapshot to revert to the original PIT
What is the relationship between linking targets and snaps?
snapshot can be linked to multiple targets but target volume can only be linked to one snap
What is the benefit of having the no copy mode linked targets in an SRP different from the source SRP?
none
writes to the source volume creates snapshot deltas which are stored in the SRP of the source volume
writes do not initiate any copy to the target
What happens once a snap has been linked to a target?
process of defining tracks for the target is initiated
What is an undefined state for a snap to target link?
location of data for the target has to be resolved through pointers for the snapshot
What is a defined state for a snap to target link?
data for the target points directly to the corresponding locations in the SRP
What is a relink operation for snapshots?
unlink the target from the current snap and links it to a different snap
What is required for a relink operation to occur?
must be between the same source and target devices
What does an unlink operation do for snapshots?
disassociates linked target from the snapshot
What OS do you need to allow access to unlinked targets?
HYPERMAX OS5977 or later
What must you do before restoring a snap to a source volume?
source volume should be unmounted prior to the restore operation and then remounted
What must you do to restore from a linked target?
a snapshot of it must be established - snapshot should be linked to source volume
What is the benefit of cascaded snaps?
provide separation and disguise presenting sensitive data
What should you be cautious of in relation to SGs and snaps?
when expanding SGs w/ existing snaps
new volumes can be added to the SGs based on the growth of the application
existing snaps do not include the new volumes
new snaps include the new volumes
What happens if you’ve recently expanded an SG and an SG is restored from an older snap?
the new volumes are set as Not Ready (NR) to the host
volumes will remain NR even after restore session is terminated - user must manually decide best action to include new volumes
What feature in relation to snaps was included in PowerMaxOS 5978?
online device expansion for local replication (LREP) configurations
admin can increase the capacity of TDEVs that are part of LREP relationship without service disruption
in the past you would need to delete an existing snap to leverage ODE
What devices are eligible for ODE?
those that are part of SnapVX sessions and legacy sessions
What happens when you terminate a snapshot?
removes it from the system
