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Dell SPEED Guru Exams > SPEED Unity > Flashcards

SPEED Unity Flashcards

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
Q

Why is IO overhead more on thin LUNs than thick LUNs?

A

must do a pointer operation that thick LUNs don’t have to do

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26
Q

How much capacity does a NAS Server take up on Unity?

A

3.5GB total (1GB of data and 2.5GB of overhead) - doesn’t grow

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27
Q

Why is maximum file performance on Unity typically half of its block performance?

A

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

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28
Q

How is data synchronized between SPs on Unity?

A

CMI interconnect

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29
Q

What is key to know about multi-core optimization for Unity?

A

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)

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30
Q

What kind of multipathing does Unity have?

A

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

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31
Q

How are NAS Servers mounted on Unity?

A

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
Q

What is the multicore functionality of Unity file?

A

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
Q

What is the benefit of LACP and Unity file?

A

provides redundancy in case of single path failure

can possibly improve performance by spreading traffic across multiple ports

34
Q

What is SP DRAM used for?

A

hold running OS
provides data cache (multi-core cache)
provides metadata cache (buffer cache)
hold other OS functions

35
Q

What is Unity multi-core cache?

A

adaptive cache used to store client data for faster access

cache space dynamically allocated between read/writes

36
Q

What is the main benefit of multi-core cache?

A

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
Q

What is the multi-core cache amount in each Unity model?

A

380 - 12GB
480 - 18GB
680 - 38GB
880 - 64GB

38
Q

What is important to understand about multi-core cache?

A

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
Q

What is contained in buffer cache?

A

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
Q

What is buffer cache also used for besides metadata cache?

A

file system data blocks - file protocols store data in buffer cache - competes w/ metadata

data reduction operations - compress/decompress and dedupe

41
Q

How much data can each GB of buffer cache handle?

A

750GB of active thin LUN capacity

180GB of active file system capacity

active capacity larger than buffer cache limits can incur IO overhead

42
Q

How much buffer cache is on each model?

A

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
Q

What is FAST Cache not suited for?

A

very random workloads over a large active capacity

44
Q

What is the decay rule for FAST VP?

A

slice temperature decays 50% every inactive 24 hours

45
Q

What are the rules for FAST VP?

A

priority given to metadata slices

considers wear levels of SSDs

46
Q

What is the performance hit by utilizing snapshots/thin clones?

A

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
Q

Why is it recommended to schedule snapshot deletion at low activity periods?

A

requires additional CPU to scan and update metadata

may also require additional drive IOPS to page metadata into buffer cache

48
Q

What role do snapshots play in asynchronous replication on Unity?

A

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
Q

What is the performance hit by utilizing asynchronous replication?

A

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
Q

What is the performance hit by utilizing synchronous replication?

A

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
Q

What is the performance hit by utilizing data reduction?

A

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
Q

What vendors are qualified for 2 way NDMP?

A

CommVault
IBM Spectrum Protect
Veritas Backup Exec/NetBackup

53
Q

What vendors are qualified for 2 way NDMP w/ tape?

A

IBM (LTO 7,8,9)

54
Q

What are the max VLANs per iSCSI port?

A

32

55
Q

Can you directly attach servers to Unity?

A

yes if both SPs are connected to the hosts and required multipathing software is in place

56
Q

What is the max raw capacity for each system?

A

380 - 2.3PBs
480 - 3.8PBs
680 - 7.5PBs
880 - 15PBs
VSA - 1PB

57
Q

What is the max LUN/consistency group count per system/per pool?

A

380 - 1000
480 - 1500
680 - 2000
880 - 6000
VSA - 64

58
Q

Max LUN size on each system?

A

physical systems - 256TBs
VSA - 16TBs

59
Q

Max pools per Unity system?

A

380 - 20
480 - 30
680 - 40
880 - 100
VSA - 16

60
Q

What is the file system size on Unity?

A

physical - 256TBs
VSA - 256TBs

61
Q

What are the max number of file systems per system?

A

380 - 1000
480 - 1500
680 - 2000
880 - 4000
VSA - 64

62
Q

What are the max number of NAS Servers per system?

A

380 - 90
480 - 128
680 - 128
880 - 256
VSA - 16

63
Q

What are the max number of file systems per NAS Server?

A

380 - 500
480 - 500
680 - 2000
880 - 4000
VSA - 64

64
Q

What are the max number of file shares per system?

A

380 - 500
480 - 1500
680 - 10000
880 - 10000
VSA - 150

65
Q

What are the maximum NAS tenants per system?

A

380 - 90
480 - 128
680 - 128
880 - 256

66
Q

What are the hierarchichal snapshot capabilities of Untiy?

A

10 levels deep for block and file

67
Q

What are the max replication sessions for Unity?

A

380 - 1000
480 - 1000
680 - 1500
880 - 1000
VSA - 32

68
Q

What are the max synchronous replication objects?

A

380 - 500
480 - 750
680 - 1000
880 - 2000

69
Q

What are the max synchronous replication consistency groups?

A

380 - 64
480 - 64
680 - 64
880 - 128

70
Q

What are the max LUNs per synchronous replication consistency group?

A

32

71
Q

What are the max LUNs per asynchronous replication consistency group?

A

75

72
Q

What is the max number of NAS Servers that can be replicated per system?

A

380 - 90
480 - 128
680 - 128
880 - 256
VSA - 4

73
Q

What is the max vVol size on Unity?

A

16TB

74
Q

What are the max vVol instances on Unity?

A

380 - 9000
480 - 9000
680 - 13500
880 - 30000

75
Q

What are the max IOPS on Unity AF models (block - file cut it in half)?

A

380 - 600K
480 - 1.68M
680 - 2.36M
880 - 2.56M

76
Q

What is the FAST Cache capacity of each hybrid model?

A

380 - 800GB
480 - 1.2TB
680 - 3.2TB
880 - 6TB

Dell SPEED Guru Exams (8 decks)

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