PS Series (EqualLogic) Storage FAQ

This article addresses frequently asked questions (FAQs) related to Dell PS Series (EqualLogic) storage.

For additional technical resources, refer to KB 124949: PS Series technical documents and videos.

See Resolution section

 

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Question: What RAID configurations do Dell PS Series (EqualLogic) arrays support?
Answer: Supported RAID configurations for PS Series arrays include the following:

• RAID10
• RAID10 (no spares)
• RAID50
• RAID50 (no spares)
• RAID5
• RAID6
• RAID6 (no spares)
• RAID6 Accelerated (only RAID level for hybrid arrays)   

RAID 5 does not offer optimal data protection for business-critical data due to the higher risks of encountering a second drive failure during a rebuild. Therefore, it is not recommended. You cannot configure RAID 5 using the Group Manager GUI, but it can be configured using the CLI.

Question: If I have multiple enclosures in a single SAN, do all enclosures need to use the same RAID type?
Answer: Each enclosure can be configured with its own RAID type. Each member can only have one RAID type. You cannot select individual drives to create different RAID levels inside one enclosure.
 

Question: Can pools span arrays?
Answer: Yes. A pool may have multiple member arrays. By default, the space is striped across them proportionally by their respective sizes.
 

Question: How is newly released functionality/software delivered? Can customers obtain this, or is that a part of maintenance? Is there a cost to new features that come out after the purchase?
Answer: Firmware (FW) updates are available on eqlsupport.dell.com. To receive FW updates, the array must be under the original one-year warranty or have a valid support contract on each array purchased.
 

Question: What software is preloaded on the array?
Answer: The array is preloaded with the firmware operating system. Firmware updates and patches can be downloaded from eqlsupport.dell.com.
 

Question: What additional PS Series software is available for the array?
Answer: The following is available for download and installation to array owners with a valid support contract (or still under warranty):

• Firmware updates
• MTU (Manual Transfer Utility)
• Dell Storage Update Manager (DSUM)
• SAN HQ (SAN Headquarters)
• HIT/ME (Host Integration Tools for Microsoft)
• HIT/LE (Host Integration Tools for Linux)
• SRA (Storage Replication Adapter for VMware) for VMware SRM (Site Recovery Manager)
• MEM (Multipathing Extension Module for VMware)
• VSM (Virtual Storage Manager for VMware)
• Dell EqualLogic Adapter for vROps (VMware vRealize Operations Manager)
• Visio stencils and links to Dell EqualLogic SCOM (Storage Management Pack Suite)

 
Question: Is it a PS Series best practice to recommend iSCSI HBAs?
Answer: Hardware iSCSI HBAs are not a requirement for PS Series arrays. The PS Series solution fully supports Ethernet NICs, TOE cards, or iSCSI-spec-compatible HBAs. HBAs offer boot-from-SAN capability, along with the potential to reduce the host CPU workload.  
 

Question: Are Jumbo frames required?
Answer: No. The PS Series array auto negotiates standard frames on a per-iSCSI session basis. Jumbo frames improve network efficiency and should be used if the switch infrastructure supports it. Even if the host does not support Jumbo frames, inter-array communication benefits from them if enabled on the network switches.


Question: Can I disable Jumbo frames on the array?
Answer: No. You cannot change the MTU size on the array. However, disabling Jumbo frames on the switch or host has the desired effect. The array always shows an MTU size of 9000. At connection time, the MTU size must be negotiated for that session.
 

Question: Is link-level flowcontrol required?
Answer: Yes, in non-DCB configurations, all array and server ports must be configured for flowcontrol.  
 

Question: Should I hard wire the speed and duplex on switch ports?
Answer: No. Auto negotiation is preferred.
 

Question: How is the back end handled in a multi-chassis environment? Is there a primary/secondary relationship to keep track of volume metadata? What happens if access to the primary array with metadata goes down?
Answer: There is no primary array; they are all peers. When you have multiple arrays in the same pool, data is striped between members, up to three members by default, or more if the volume size does not fit on three members. In that case, if you lose any member with data for a given set of volumes, those volumes go offline until the member is restored.
 

Question: Can any of the hard drives be set up as a hot spare?
Answer: Yes. Depending on the RAID level it may be one, two, or optionally none.
 

Question: Does the array do global hot sparing or only in the chassis they are in?
Answer: Hot spares are only available to the chassis they are in.
 

Question: Where is the ACL (access control list) kept?
Answer: The ACL is on the array.
 

Question: If all arrays are peers and iSCSI is a point-to-point connection, how does the server access the right array that has the right part of its data?
Answer: The host maps to the volume through access control lists for that volume and volume data is spanned across the arrays in a pool. When the server connects to a physical array port, and there is data on another member for that volume, a hidden MESH connection is created to the other member(s). Data to or from that member uses that inter-member MESH connection.  
 

Question: How is an I/O (either read or write) is fulfilled? Which array responds to a server request if many arrays have parts of that volume?
Answer: The array on which the data resides responds to the request.  
 

Question: In a read/write operation, which array gets the request?
Answer: If the HIT ME/LE or MEM for ESXi is installed on the host, all write and read operations are delivered from the member containing the data. MEM/HIT allows a connection to all the members with data for that volume, and the requests are directly routed to the correct member. Without HIT/MEM installed, if the server has established and connects to member A, and if the data is on another member, a hidden connection known as the MESH" connection between members is used to get that data on the other member, then the data is passed on to the server through that established iSCSI connection. That same MESH connection is used to send data to the member that needs it.