Top 35 Emc Symmetrix Interview Questions You Must Prepare 16.Aug.2022

Symmetrix Optimizer improves array performance by continuously monitoring access patterns and migrating devices (Symmetrix logical volumes) to achieve balance across the disks in the array. 

Step 1: Symmetrix Optimizer builds a database of device activity statistics on the Symmetrix back-end. 

Step 2: Using the statistical data collected, configuration information, and the user-defined parameters, the Optimizer algorithm identifies busy and idle devices and their locations on the physical drives. The algorithm tries to minimize average disk service time by balancing I/O activity across physical disks. Optimizer determines which disks require balancing by locating busy devices close to each other on the same disk, and/or by locating busy devices on faster disks or faster areas of the disks. Optimizer takes into account the speed of the disk, the disk geometry, and the actuator speed to determine faster disks. 

Step 3: Once a solution for load balancing has been developed, the next phase is to carry out the Symmetrix device swaps. This is done using established Time Finder technology, which maintains data protection and availability. We can specify whether swaps should occur in a completely automated fashion, or if the device swaps require user approval before the action is taken. 

Step 4: Once a swap function completes, Symmetrix Optimizer continues data analysis for the next swap.

We cannot create Disk Groups; it should be done by changing BIN file by CE. 

We can rename the existing disk groups. 

Example: symconfigure -Sid 207 -cmd “set disk_group 4 disk_group_name = flash_dsks;” -v -nop commit.

To monitor real time 100 event records with 600 seconds interval in the symmetrix array. 

Symevent -sid 4282 monitor -i 600 -c 100 -warn/-error/-fatal.

To create access control list on symmetrix array to implement host level or user level security.

Stripped Meta Devices: 

Meta device addressing by striping divides each Meta member device into a series of stripes, addressing a stripe from each device before advancing to the next stripe on the first device. When writing to a striped volume, equal size stripes of data from each participating drive are written alternately to each member of the set. 

Concatenated Meta Devices: 

Concatenated devices are volume sets that are organized with the first byte of data at the beginning of the first device. Addressing continues to the end of the first device before any data on the next device is referenced. When writing to a concatenated device, the first meta device member receives all the data until it is full, and then data is directed to the next member and so on.

This feature will automatically selects and assigns the LUN IDs to the devices while device mapping to the port Instead of manually assigning address to the device while mapping.

  • Low-level I/O commands executed using SYMCLI are routed to the Symmetrix array by a Symmetrix storage device that is specified as a gatekeeper. 
  • The gatekeeper device allows SYMCLI commands to retrieve configuration and status information from the Symmetrix array without interfering with normal Symmetrix operations. 
  • The gatekeeper must be accessible from the host where the commands are being executed.

It is a database file in the host which stores the symmetrix array configuration data.

Can be used to get the configuration data offline.

Maximum Cylinders = 65520 

Maximum Capacity = 59GB or 61425 MB

  • Creating Thin Pools. 
  • Creating Data devs and added these Data devs to Thin Pools. 
  • Creating DEVs and bind these DEVs to Thin Pool. 
  • Assign DEVs to host.

  • The preview argument verifies the syntax and correctness of each individual change defined, and then terminates the session without change execution. 
  • The prepare argument performs the preview checks and also verifies the appropriateness of the resulting configuration definition against the current state of the Symmetrix array; the argument then terminates the session without change execution.
  • The commit argument completes all stages and executes the changes in the specified Symmetrix array.

  1. by using EMC Control Center 
  2. by using symcli commands Symcfg and Symdisk

Symcfg -Sid 4282 list -connections -capacity 

Copy and paste the output of the above command in excel file and format according to the requirement.

Set up or update the Symmetrix array user authorization information.

  • To measure changes to data on a Symmetrix volume or group of volumes. 
  • Change Tracker data is often used to analyze and design Time Finder and Symmetrix Remote Data Facility (SRDF) configurations. 
  • Change Tracker (Delta Mark) session must be created using the symcli create command. The symchg mark command is then used to perform a timestamp and mark the selected area of disk storage occupied by a data object using a Delta Mark bitmap.

  • To show the details about audit log itself. 
  • Symaudit -Sid 4282 show. 
  • To list the audit log records of specific period of time. 
  • Symaudit -Sid 4282 list -v -start time 7/11:9:00 -end time 7/11:10:00 
  • To monitor the real time audit logs 100 records with 30sec interval. 
  • Symaudit -Sid 4282 monitor -i 30 -c @

By Disk Group: Symdisk -Sid XXXX list -by_diskgroup.

Array as whole: Symconfigure -Sid XXXX list –freespace.

User-to-role mappings have to be created: 

(Create a command file with the following entry (ex: rolemap.txt)) 

Assign user H: Host username to role Monitor; 

Assign user D: Eng username to role Admin; 

(Execute the above file) 

Symauth -sid 4282 -f rolemap.txt commit. 

(Roles: None, Monitor, Storage admin, admin, Auditor, SecurityAdmin) 

Enable the user authorization: 

Symauth -Sid 4282 enable.

Symacl -sid 4282 backup -file "command file" 

Symacl -sid 4282 commit -restore -f command file

  • Let us assume cable connectivity is done properly. 
  • Install HBA drivers in host. 
  • Install Power path if required. 
  • Check that the HBA ports are showing online. 
  • Create zoning at switch end. 
  • Check that this host is logged in to the Storage array 
  • Create LUN/hyper in storage array. 
  • Form Meta devices if required. 
  • Map the devices to the FA port. 
  • Mask the devices to the host hba (wwn). 
  • Refresh the Array to affect the changes.

The device masking database (VCMDB) holds device masking records and typically resides on a 24 or 48 cylinder disk device. 

Symmaskdb -Sid XXXX backup -f filename.

  1. Power path - host end 
  2. Time Finder - local replication 
  3. SRDF - Remote Replication

256 LUN IDs are available per FA port, 255 LUN IDs are usable out of 256.

Vault Drivers: At the time of emergency shutdown of an Array, whatever the data in cache memory will be destaged/saved on temporary drives called vault drives.

Hot Spare: At the time of physical drive failure hot spare drives will take place.

Symcfg -Sid XXXX -SA all list -v 

Set Symmetrix MatricName=MatricValue

  • It depends on the Symmetrix management applications using in management servers.
  • As per EMC recommendations 6 gatekeepers are required per management host using symcli.

Symmetrix external locks are used by SYMAPI (locks 0 to 15) and also for applications assigned by EMC (>15) to lock access to the entire Symmetrix array during critical operations.

  • We can check the external locks by giving the below command 
  • Symcfg -Sid XXXX list -lockn 
  • We can check the external locks by giving the below command 
  • Symcfg release -Sid -lockn 15 -force

Quality of Service (QoS) allows more flexibility in managing Symmetrix system’s performance. By increasing the response time for specific copy operations on selected devices, we can increase the overall performance of the other Symmetrix devices. 

  • The QoS (Quality of Service) feature allows us to adjust the data trfer pace on specified devices, or devices in a device group, for certain operations. 
  • The contention for cache access can be quality of service managed by the least recently used (LRU) ring partitions in the Symmetrix cache. 
  • We can control the priority service time of devices and control cache partitions for different device groupings.

Using Performance Monitoring feature in EMC Control Center. 

Using SYMSTAT symcli command.

Thin provisioning is a method of optimizing the efficiency with which the available space is utilized in storage area networks. Thin provisioning operates by allocating disk space in a flexible manner among multiple users, based on the minimum space required by each user at any given time.

REQUESTS: Reports I/O requests and throughput for selected devices, directors, or SRDF/a session. (This is the default type; if no type is specified REQUESTS is used.) 

BACKEND: Reports back-end I/O requests and throughput for selected devices. 

PORT: Reports performance statistics for a director port. ISCSI Report Gig-E network statistics. 

CACHE: Reports cache activity for selected front-end or remote link directors, or SRDF/A sessions. 

MEMIO: Reports cache memory to disk activity for selected devices. PATH Report R-Copy path information for no incremental sessions. Symmetrix arrays that have all or some incremental sessions will report an error. 

CYCLE: Report cycle summary information for SRDF-A sessions. 

DISK: Reports back-end I/O requests and throughput for selected disks. 

PREFETCH: Reports track prefetch disk activity for selected back-end director’s only.DMSP Reports dynamic mirroring service policy (DMSP) statistics for the selected device(s). 

RDF: Reports SRDF statistics from the perspective of RA groups, devices, or directors.

  • A QoS feature, dynamic cache partitioning allows the Administrator the me to dynamically control the cache area size, servicing a given device group I/O, by defining flexible partitions through cache memory. 
  • Dynamic Cache Partitioning divides the cache memory into multiple partitions with unique names and their device path assignments. 
  • Partition areas can be made static or dynamic in size. The dynamic partitioning provides flexibility to the amount of floating memory that can be allocated with a high and low watermark. This allows memory resources to be temporarily donated to other partitions when needed. 
  • The symqos command allows you to create partitions for different device groupings in addition to the default partition that all devices belong to initially. Each partition will have a target cache percentage as well as a minimum and maximum percentage. In addition, you can donate unused cache to other partitions after a specified donation time.

  • Host-end logs are available in Symapi log folder 
  • Event logs and Audit logs in symmetrix array

Symauth -Sid 4282 backup -f backupfile.cmd commits 

Symauth -Sid 4282 restore -f backupfile.cmd commit

To list all events in symmetrix array 

Symevent -Sid 4282 list 

To list specific period of time events in event logs 

Symevent -Sid 4282 list -vs -start 9:00 -end 17:00

  • Check that the host is logged in to the Array.
  • Check that the cable connectivity status by logging in to the host. 
  • Check that the HBA drivers are properly configured. 
  • Check the Zoning table by logging in to the switch. 
  • Check that the devices status in Array. 
  • Check the VCMDB for masking information, etc…