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Dell SPEED Guru Exams > SPEED Unity > Flashcards

SPEED Unity Flashcards

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1
Q

What is the buffer cache size of each system?

A

380 - 33.5GB
480 - 55GB
680 - 112GB
880 - 244GB

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2
Q

What is the core count of each system

A

380 - Intel Broadwell 6 core
480 - Intel Skylake - 16 core
680 - Intel Skylake - 24 core
880 - Intel Skylake - 32 core

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3
Q

What is the front end connectivity of the 480 and higher?

A

8 x 10GbE or 8 x 25GbE optical - additional connectivity requires IO modules

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4
Q

How would you go about increasing bandwidth or drive count on a Unity 480 or higher?

A

adding SAS Buses

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5
Q

What benefit does write caching have on performance?

A

2 x CNA (FC or Ethernet) per SP

2x 10G BASE-T per SP

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6
Q

What are all the IO modules available for Unity?

A

4 port 32Gb FC
4 port 10Gb Base T
4 port 10GbE optical
4 port 25GbE optical
4 port 12Gb/s SAS (only for 480+)

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7
Q

What are the benefits of adding the 4 port SAS backend 12Gb module?

A

adds up to 4 more Buses

for systems that require more than 500 drives

can also increase max available bandwidth

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8
Q

What is a drawback of adding the 4 port backend module?

A

it takes up an expansion slot so leaves only two (1 pair)

shifts bottleneck to front end by limiting front end expandability

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9
Q

What do flash drives love for maximum performance?

A

queues

ability to process long queues and handle IO internally in parrallel

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10
Q

What is the relationship between DAEs and SAS Buses?

A

using only the drives in the DPE means only 1 SAS bus is active

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11
Q

What is true about small Unity configurations?

A

will almost always be drive bound by number of drives when it comes to performance

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12
Q

What is the benefit of adding front end IO Modules?

A

allows greater bandwidth and IOPS between clients and Unity

more efficiently spreads load across Unity ports and CPU

also improves availability through multi-pathing capabilities

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13
Q

What are the best practices for Unity hardware?

A

use as many front end ports as possible (spread workload across all available ports)

use all available back-end SAS Buses (cables DAEs to both on-board SAS ports - if SAS IO Module is installed cable DAEs to all 6 buses)

spread flash drives across all available Buses

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14
Q

When should you use 10K SAS drives vs NL-SAS drives for performance reasons?

A

10K SAS = good overall performance

NL-SAS = good for high bandwidth - use for large IO and sequential access

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15
Q

What is the general rule when it comes to selecting RAID widths?

A

smaller RAID widths have slightly better performance and availability

larger RAID widths have better usable capacity

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16
Q

What are the supported RAID widths in Unity XT?

A

RAID 5 = 4+1, 8+1, 12+1
RAID 6 = 4+2, 6+2 10+2 12+2, 14+2
RAID 1/0 = 1+1, 2+2, 3+3, 4+4

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17
Q

What is the rule with dynamic pools and RAID width?

A

will adopt the largest stripe width possible with the drive count used to create the pool

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18
Q

What is the required space allocation for metadata on Unity?

A

1-3%

fixed amount per object - variable amount as object grows

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19
Q

How is metadata stored on Unity?

A

physically separates all metadata from user data by placing them on separate slices within pool

metadata slices placed in highest tier (even if actual data is residing on Lowest Available tier)

FAST VP will promote any metadata slices that get allocated to lower tiers

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20
Q

What is true about RAID in Unity pools?

A

cannot change RAID type but can change RAID widths between drives in each pool

not optimal

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21
Q

What do the system drives store in Unity?

A

persistent database (system configuration)

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22
Q

What is the benefit of promoting metadata to flash?

A

removes most of the metadata lookup latency from the IO path

removes the metadata operations from spinning disks

allows for better optimizations for data access on spinning disk

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23
Q

What is true about thick LUNs on Unity?

A

same metadata capacity overhead as thin LUNs but provide lower IO overheads w/ less block map lookup required,

but also have no snapshot, replication, or DR capability

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24
Q

What is the result of thin LUNs having more IO overhead than thick LUNs?

A

increases CPU utilization and possible back-end drive IOPS

for systems that are CPU or drive bound - thin LUNs will have less performance

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25
Why is IO overhead more on thin LUNs than thick LUNs?
must do a pointer operation that thick LUNs don't have to do
26
How much capacity does a NAS Server take up on Unity?
3.5GB total (1GB of data and 2.5GB of overhead) - doesn't grow
27
Why is maximum file performance on Unity typically half of its block performance?
file system access can result in multiple indirect access writes can incure additional overhead as file metadata is updated unity file systems require buffer cache for both data and metadata so they compete
28
How is data synchronized between SPs on Unity?
CMI interconnect
29
What is key to know about multi-core optimization for Unity?
for block protocols specifically assigns a single CPU core to service all IO on a given front end port (IO processing most efficient when completely serviced by the same core)
30
What kind of multipathing does Unity have?
FE - IO redirection between SPs to improve availability BE - both SPs have direct SAS connections to drives - CMI can transfer data for higher efficiency between SPs
31
How are NAS Servers mounted on Unity?
serviced by single SP - all file systems associated w/ that NAS Server serviced by that SP NAS Servers and file systems can auto-failover if necessary
32
What is the multicore functionality of Unity file?
maintains a pool of threads for each protocol (NFS/SMB) protocol threads distributed across cores - any thread can service any IO to balance core utilization
33
What is the benefit of LACP and Unity file?
provides redundancy in case of single path failure can possibly improve performance by spreading traffic across multiple ports
34
What is SP DRAM used for?
hold running OS provides data cache (multi-core cache) provides metadata cache (buffer cache) hold other OS functions
35
What is Unity multi-core cache?
adaptive cache used to store client data for faster access cache space dynamically allocated between read/writes
36
What is the main benefit of multi-core cache?
provides durable write caching provides better response time for read cache hits write data remains in memory for cache rehits pre-fetch and read ahead attempt to stage data in cache for sequential and large block IO
37
What is the multi-core cache amount in each Unity model?
380 - 12GB 480 - 18GB 680 - 38GB 880 - 64GB
38
What is important to understand about multi-core cache?
it's a unified cache shared by each SP no segmentation between reads/writes a cache page used for writes is mirrored to peer a cache page used for read can be accessed by either SP for cache hit (transferred over CMI)
39
What is contained in buffer cache?
metadata which has previously been retrieved from the storage pool goal is to eliminate backend IO for metadata lookups managed on an LRU basis
40
What is buffer cache also used for besides metadata cache?
file system data blocks - file protocols store data in buffer cache - competes w/ metadata data reduction operations - compress/decompress and dedupe
41
How much data can each GB of buffer cache handle?
750GB of active thin LUN capacity 180GB of active file system capacity active capacity larger than buffer cache limits can incur IO overhead
42
How much buffer cache is on each model?
380 - 62GB (46.5TB LUN / 11.16TB FS) 480 - 102GB (76.5TB LUN / 18.36TB FS) 680 - 212GB (159TB LUN / 38.16TB FS) 880 - 462GB (346.5TB LUN / 8316TB FS)
43
What is FAST Cache not suited for?
very random workloads over a large active capacity
44
What is the decay rule for FAST VP?
slice temperature decays 50% every inactive 24 hours
45
What are the rules for FAST VP?
priority given to metadata slices considers wear levels of SSDs
46
What is the performance hit by utilizing snapshots/thin clones?
require allocating a write - new data block must be allocated to hold new data + metadata must be updated to track new block additional CPU and memory are used additional drive IOPS are generated internal write latency impact = affect front end IO writes
47
Why is it recommended to schedule snapshot deletion at low activity periods?
requires additional CPU to scan and update metadata may also require additional drive IOPS to page metadata into buffer cache
48
What role do snapshots play in asynchronous replication on Unity?
utilizes snaps on source and destination snaps determine which data has changed since the last refresh snaps provide roll-back capability in case of loss connectivity
49
What is the performance hit by utilizing asynchronous replication?
since it uses snapshots expect performance hit from snaps additional read activity when data transfer occurs data transfer rates may be limited by network connectivity multiple replication sessions can transfer data simultaneously increasing data transfer rate (splitting source object into multiple independent objects can make replication faster)
50
What is the performance hit by utilizing synchronous replication?
host write IOs will see increased latency - additional latency will depend on distance of systems only a single FC link exists between source and destination SPs (pair of links per Unity system)
51
What is the performance hit by utilizing data reduction?
additional CPU and memory are used to rehydrate data during reads of reduced data (tracking metadata + running rehydration algorithm) system becomes CPU saturated with lower overall workload due to additional cycles needed for data reduction/rehydration
52
What vendors are qualified for 2 way NDMP?
CommVault IBM Spectrum Protect Veritas Backup Exec/NetBackup
53
What vendors are qualified for 2 way NDMP w/ tape?
IBM (LTO 7,8,9)
54
What are the max VLANs per iSCSI port?
32
55
Can you directly attach servers to Unity?
yes if both SPs are connected to the hosts and required multipathing software is in place
56
What is the max raw capacity for each system?
380 - 2.3PBs 480 - 3.8PBs 680 - 7.5PBs 880 - 15PBs VSA - 1PB
57
What is the max LUN/consistency group count per system/per pool?
380 - 1000 480 - 1500 680 - 2000 880 - 6000 VSA - 64
58
Max LUN size on each system?
physical systems - 256TBs VSA - 16TBs
59
Max pools per Unity system?
380 - 20 480 - 30 680 - 40 880 - 100 VSA - 16
60
What is the file system size on Unity?
physical - 256TBs VSA - 256TBs
61
What are the max number of file systems per system?
380 - 1000 480 - 1500 680 - 2000 880 - 4000 VSA - 64
62
What are the max number of NAS Servers per system?
380 - 90 480 - 128 680 - 128 880 - 256 VSA - 16
63
What are the max number of file systems per NAS Server?
380 - 500 480 - 500 680 - 2000 880 - 4000 VSA - 64
64
What are the max number of file shares per system?
380 - 500 480 - 1500 680 - 10000 880 - 10000 VSA - 150
65
What are the maximum NAS tenants per system?
380 - 90 480 - 128 680 - 128 880 - 256
66
What are the hierarchichal snapshot capabilities of Untiy?
10 levels deep for block and file
67
What are the max replication sessions for Unity?
380 - 1000 480 - 1000 680 - 1500 880 - 1000 VSA - 32
68
What are the max synchronous replication objects?
380 - 500 480 - 750 680 - 1000 880 - 2000
69
What are the max synchronous replication consistency groups?
380 - 64 480 - 64 680 - 64 880 - 128
70
What are the max LUNs per synchronous replication consistency group?
32
71
What are the max LUNs per asynchronous replication consistency group?
75
72
What is the max number of NAS Servers that can be replicated per system?
380 - 90 480 - 128 680 - 128 880 - 256 VSA - 4
73
What is the max vVol size on Unity?
16TB
74
What are the max vVol instances on Unity?
380 - 9000 480 - 9000 680 - 13500 880 - 30000
75
What are the max IOPS on Unity AF models (block - file cut it in half)?
380 - 600K 480 - 1.68M 680 - 2.36M 880 - 2.56M
76
What is the FAST Cache capacity of each hybrid model?
380 - 800GB 480 - 1.2TB 680 - 3.2TB 880 - 6TB

Dell SPEED Guru Exams (8 decks)

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