ArcaOS can directly access HDDs and SSDs of up to 2 terabytes (TiB) in size. This means that a 6TiB drive may be used, but AcaOS will only “see” the first 2TiB of space on the drive, and the drive may be unsuitable for multi-boot configurations (surely, ArcaOS and any volumes accessed by ArcaOS will have to be created within the 2TiB boundary). In short, these larger drives should currently be avoided for use with ArcaOS.
ArcaOS includes disk drivers for IDE, AHCI, and SCSI controllers. (SATA “Legacy mode” utilizes the IDE driver, whereas SATA “Native mode” utilizes the AHCI driver. SCSI drivers are manufacturer and model-specific.)
Currently, SAS and NVMe are not supported. Unsupported disk devices will be silently ignored by ArcaOS, so in multiboot scenarios, it is possible to have another operating system boot from an unsupported device. ArcaOS, however, will be unable to access any data on such a device, even if the underlying filesystem would otherwise be readable by ArcaOS. In short, these devices are simply invisible to ArcaOS.
Hardware RAID devices which are driver-less are supported, as are SATA and SCSI RAID devices where a native driver is available (either provided with ArcaOS or available from a third party).
A note about connection types and device dimensions
HDDs and SSDs may connect to the system through a variety of methods. IDE uses a 40-pin connector, which is known as PATA (Parallel ATA), whereas SCSI will typically use a 50 or 68-pin connector. SATA (Serial ATA) uses a flat, 7-conductor connector.
Both HDDs and SSDs come in a variety of physical sizes. Generally, HDDs today are 3.5 inches wide for desktops and servers and 2.5 inches wide for laptops. SSDs may be packaged in 2.5-inch cases and connect just like a SATA HDD, or may come as circuit boards with exposed memory chips.
For internal connection, these boards generally utilize an M.2 (formerly known as Next Generation Form Factor, or NGFF) connector, which provides a slot into which the end of the SSD board is inserted. Note that the M.2 specification may be used for AHCI as well as NVMe devices. As stated earlier, ArcaOS currently does not support NVMe. An M.2-connected SATA drive should be recognized and work normally with ArcaOS, however.
It is often (wrongly) said that a system has an “M.2 drive.” M.2 is a form factor and connector specification, and not a drive specification.
ArcaOS requires disk devices to utilize 512 bytes per sector (traditional) formatting. Many new SSDs utilize Advanced Format (AF) which refers to sectoring larger than 512 bytes. SSDs which provide 4K native (4Kn) sectoring must provide 512-byte emulation (512e) to mimic a traditional drive. Most AF drives do provide this functionality. Check the manufacturer’s specifications if unsure.
Drive Geometry (CHS)
ArcaOS views hard disks in terms of Cylinders, Heads, and Sectors (CHS), instead of the alternative Logical Block Addressing (LBA) method. When a disk is larger than 512GB, ArcaOS uses a hard disk geometry which has a sectors per track (SPT) value larger than the usual 63 SPT. Depending on the size of the hard disk, the value for SPT may be 127 or 255. This extended value is recorded in the LVM information on the hard disk and it is usually not recognized by other operating systems or their partitioning tools.
Specifically, the SPT requirements for disks larger than 512GB for use with ArcaOS are:
- Disks < 502GiB can use 63 SPT, 127 SPT, or 255 SPT
- Disks > 502GiB and < 1TiB can use 127 SPT or 255 SPT
- Disks > 1TiB must use 255 SPT
Windows-created disks use 63 SPT for all sizes, thus Windows-created disks larger than 502GiB are unsuitable for use by ArcaOS unless or until a full backup/wipe/repartition/restore is done. (See the section below on GPT vs MBR for further thoughts when considering this type of operation.)
If you are planning to add ArcaOS as an additional operating system to a PC which is running a version of Windows 7 or higher, it is possible that the disk has been partitioned using a GUID Partition Table (GPT) instead of a Master Boot Record (MBR) scheme. ArcaOS requires MBR partitioning, and will not install to a GPT disk. Further, ArcaOS cannot access data stored on GPT disks.
How to tell whether the current disk layout is GPT or MBR
Under Windows, the easiest way to tell is to open Disk Management, select the disk, right-click, and select Properties. On the Volumes tab, there should be an item labeled Partition style. This will indicate whether the disk is GPT or MBR.
For Linux installations, consult the documentation for your distribution.
Changing partitioning schemes generally involves a complete backup/wipe/repartition/restore procedure. Often, this is a good time to consider the age of the disk, its capacity, and whether it might be easier to copy the existing partitions to a new MBR device using a suitable utility, such as DFSee.
The Logical Volume Management (LVM) system of ArcaOS expects partitions to be CHS-aligned, a requirement which may not be met if the disk was originally (or last) partitioned by foreign (non-OS/2-aware) partitioning software.
Many modern systems often come with hard disks partitioned using MiB alignment and accompanying partitioning tools often use the MiB alignment method as the default. This alignment method is not compatible with ArcaOS. To correct this, a full backup/wipe/repartition/restore is required. (See the section above on GPT vs MBR for further thoughts when considering this type of operation.)