The IBM 1746-C4A is the dual-controller version of IBM’s DS3524 Express, an older 2U shared-storage array with 24 2.5-inch SAS bays. IBM commonly maps this configuration to product number 1746A4D; the single-controller version is 1746A4S. It can be a useful low-cost lab or legacy-SAS platform, but it is not a sensible default for new production storage in 2026 because its hardware, firmware, management software and replacement-part ecosystem are obsolete.
What is the IBM 1746-C4A?
It is a rack-mounted block-storage array in IBM’s DS3500 family, not a general-purpose server and not a NAS appliance. The system presents RAID-protected logical volumes to connected hosts over a storage fabric or direct-attached link. Normal SMB and NFS file shares require a separate server or NAS layer.
IBM’s compatibility listing identifies the DS3524 Express Dual Controller Storage System as machine type 1746, model C4A, with marketing/part number 1746A4D. The corresponding single-controller configuration is 1746A4S.
Decode the common identifiers
| Identifier | Meaning |
|---|---|
| IBM System Storage DS3524 Express | Product family and 2U enclosure |
| 1746 | IBM machine type |
| C4A | Standard AC-powered model designation |
| 1746A4D | Dual-controller product/marketing number |
| 1746A4S | Single-controller product/marketing number |
| EXP3524, 1746-E4A/1746A4E | Related 24-bay expansion enclosure family |
| C4T, 1746T4D | Separate DC-powered dual-controller DS3524 variant |
Do not treat C4A and the DC-powered 1746T4D as interchangeable descriptions. IBM’s DC announcement describes the DC model’s own power, port and cache configuration.
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IBM 1746-C4A specifications
| Item | What is established |
|---|---|
| Form factor | Rack-mounted 2U DS3524 enclosure |
| Drive bays | 24 hot-swappable 2.5-inch SAS bays |
| Controllers | Two in the C4A/1746A4D configuration |
| Disk back end | 6 Gb SAS generation, according to IBM’s DS3500 documentation |
| Host connectivity | 6 Gb SAS, 8 Gb Fibre Channel or 1 Gb iSCSI options were available; the installed interface cards determine the actual protocol |
| Expansion | EXP3524 24-bay expansion family; AC and DC versions must be matched correctly |
| Storage role | Shared block storage using RAID logical volumes, not native file sharing |
| Management | IBM DS Storage Manager, with version compatibility tied to controller firmware and host environment |
IBM’s DS3500 overview documents the SAS, Fibre Channel and iSCSI connectivity options: IBM DS3000 family overview. A model name alone does not prove which card is installed, so request rear-panel photographs before buying.
What dual-controller operation provides
Two controllers provide redundant storage-controller paths and are intended to support failover and multipath access. A host with correctly configured multipath software can continue using its volumes when one controller or path is unavailable, and maintenance can be less disruptive than on a single-controller array.
This is not end-to-end high availability. Effective redundancy also requires:
- Multipath software configured on every host.
- Separate cables and, where applicable, separate HBAs, switches and transceivers.
- Healthy power supplies, fans, cache-protection components and backplane.
- Compatible controller firmware, volume ownership and failover settings.
A shared enclosure or backplane failure can still take both controllers and all attached volumes offline.
Drive support and historical firmware requirements
The DS3524 family supported enterprise SAS, nearline SAS and self-encrypting drive options. IBM later documented 200 GB and 400 GB 2.5-inch SAS SSDs and 900 GB 10,000-rpm 2.5-inch 6 Gb SAS disks. For those later options, IBM specified controller firmware 07.77 or later and DS Storage Manager 10.77 or later in Hardware Announcement 111-149.
Those are historical qualification details, not a promise that any current SAS disk will work. Compatibility can depend on drive firmware, sector format, capacity, SAS generation, dual-port capability, carrier, controller firmware and whether IBM qualified the drive. A disk that physically fits may still be rejected or unsafe to use.
Host interfaces: SAS, Fibre Channel and iSCSI
DS3500 systems could be ordered with different host-interface cards. Depending on the installed controller hardware, a unit may be:
- 6 Gb SAS-attached: typically direct-attached to compatible server HBAs.
- 8 Gb Fibre Channel: normally used through FC switches or direct FC connections.
- 1 Gb iSCSI: presented over Ethernet using the array’s iSCSI interfaces.
“Dual controller” does not identify the protocol. Ask for clear photographs of both controller backs, daughter cards, ports and any SFPs. A listing without those details may be a bare chassis, an array missing interface cards, or a configuration unusable with your hosts.
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Expansion with the EXP3524
The matching expansion family is the IBM EXP3524, commonly identified as 1746-E4A or 1746A4E. IBM’s lifecycle page identifies the EXP3524-E4A as having reached end of support on January 31, 2019; that date applies to the expansion unit and should not be substituted for an exact C4A lifecycle record. See IBM’s EXP3524 information.
The DC announcement describes a DS3524 DC configuration supporting up to 96 drives through attached EXP3524 DC units. That figure belongs to the cited DC configuration; do not assume it is the expansion limit for every AC-powered C4A without confirming the relevant model documentation, cabling and firmware.
Management software and licensed features
DS Storage Manager configures arrays, pools or RAID groups and logical volumes. It is separate from host multipath software, controller firmware and drive firmware. IBM’s historical installation and maintenance material is available on the DS3500/EXP3500 guide page.
Depending on model, firmware and license keys, DS3500 systems offered features such as FlashCopy snapshots, VolumeCopy, remote mirroring, partition upgrades, cache upgrades and full-disk encryption. A second-hand unit may not include those licenses. Verify the keys and entitlement before relying on any feature, especially after a controller replacement or reset.
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Is the IBM 1746-C4A still supported?
It is an obsolete platform for normal IBM maintenance purposes. IBM’s lifecycle definition describes end of support as withdrawal of standard technical, field and parts support. The related EXP3524 date above confirms the generation’s age, but it is not the exact C4A end-of-support date.
In practical terms, expect no normal IBM product-development path, modern security update stream or predictable supply of genuine replacement parts. Current VMware, Windows Server, Linux, HBA, FC-switch and browser compatibility must be checked for the exact versions you plan to use; powering on is not the same as having a supported storage system.
Buying a used IBM 1746-C4A
Confirm the exact identity
- Request photographs of the bezel, drive bays, rear of both controllers and machine-type/model labels.
- Confirm 1746-C4A/1746A4D, not single-controller 1746A4S, DC 1746-T4D, EXP3524, or a bare chassis.
- Identify every host-interface card and confirm it matches your SAS, FC or iSCSI requirement.
Confirm what is included
- Two functioning controllers and two power supplies.
- Correct 2.5-inch carriers, disks or blanks, rails and power cords.
- Required SAS, FC or Ethernet cables and SFPs.
- Cache configuration, license keys and management access.
Require operating evidence
- Successful boot with no unresolved critical alerts.
- Healthy fans, power supplies, cache batteries or other protection components.
- Drive health, media-error status and controller/drive firmware versions.
- Working access to management software and both controller paths.
- Removal of previous ownership credentials or a documented reset state.
Used listings from Flagship Technologies and Vibrant Technologies illustrate why included hardware must be verified; listing availability and configuration change. There is no dependable current manufacturer price. Total cost depends on disks, cards, licenses, trays, shipping, testing and warranty.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Common operational risks
Controller batteries and cache protection
Old cache batteries can trigger faults, disable write caching or reduce performance. Overriding cache-protection warnings increases risk. Use the IBM maintenance documentation for the exact replacement procedure rather than improvising.
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Firmware and foreign metadata
IBM’s recommended drive-firmware guidance shows that drive firmware is a compatibility issue, not merely a speed setting. Used disks may also retain foreign array metadata. Clearing, initializing or reconfiguring them can destroy recoverable information, so back up data and document the existing configuration first.
Controller replacement and multipathing
A replacement controller may require matching firmware, cache, interface hardware and configuration metadata. Before any controller, firmware or volume change, back up elsewhere, record mappings and firmware versions, verify multipath behavior, change one item at a time and keep a rollback plan.
Is it worth buying in 2026?
| Use case | Verdict |
|---|---|
| Production primary storage | Generally no; unsupported hardware and parts risk outweigh the low purchase price. |
| Noncritical backup target | Only with independent backups and acceptance of recovery risk. |
| Homelab or SAN training | Potentially worthwhile if complete, tested and inexpensive. |
| Cheap legacy SAS storage | Possibly, where compatible hosts and replacement parts are already available. |
| Modern virtualization platform | Usually a poor fit because host and management compatibility is uncertain. |
| File-server or NAS replacement | Wrong product category; it provides block storage, not native SMB/NFS shares. |
Electricity for a 2U chassis populated with spinning disks, shipping, cables, HBAs, switches, replacement drives, licenses and eventual migration can exceed the acquisition price. IBM’s historical storage terms listed three years of parts-and-labor warranty for DS3000 Series equipment, but that does not create current coverage.
Alternatives by requirement
Supported shared block storage
Compare a currently supported entry-level SAN from Dell Technologies, Hewlett Packard Enterprise, Lenovo, NetApp or another vendor on controller failover, current SAS/NVMe media, 10/25 GbE or modern Fibre Channel, snapshots, replication, warranty and host compatibility. Exact model and price choices require a current product-specific evaluation.
File storage or backup shares
If the requirement is SMB/NFS, backup repositories or media storage, a modern NAS may be simpler and more appropriate. That changes the protocol and architecture rather than serving as a drop-in DS3524 replacement.
Lab learning
A newer used array with better community documentation, a server with a modern HBA and ZFS, or a small redundant NAS may provide a lower-risk way to learn storage, depending on whether the goal is SAN multipathing, RAID, virtualization or file services.
The Bottom Line
Buy an IBM 1746-C4A only when it is a complete, tested dual-controller unit with the required interface cards, documented firmware, compatible drives and a meaningful return policy—and only for workloads that can tolerate legacy hardware risk. For new production storage, choose a currently supported SAN, NAS or software-defined platform instead.
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