Unraid Cache Pool Sizing + SSD Endurance Calculator

This Unraid cache pool sizing calculator recommends cache drive capacity based on your daily ingest rate, mover schedule, and whether you want SSD endurance estimates. Helps you avoid undersizing cache and stalling writes to your array.

Your Unraid cache pool is doing more work than you might think, and if it's sized wrong or the mover is misconfigured, you're either wearing out your SSDs faster than necessary or letting your cache fill up and stall writes. This tool helps you size the pool for your actual ingest patterns, estimate how long your SSDs will last, and check whether your mover setup is working for you or against you.

Your Setup

How much new data do you write to the server per day (total ingest)?

Include writes to shares set to cache Yes/Prefer, downloads, appdata, media imports. Exclude reads and data already on the array.

GB / day

50 GB

Write pattern

Peak ingest events

Mover schedule

Pool layout

BTRFS RAID5/6 is experimental and not recommended by the Unraid team, it is not shown as an option here. Unraid cache pool docs.

Filesystem

Fixed components (live on cache permanently, never moved to array)

Docker / containers

/var/lib/docker + container volumes. Typical: 20-100 GB.

Appdata / config

/mnt/user/appdata: Plex metadata, databases. Typical: 50-300 GB.

VM disk images

Total of all VM disk images stored on cache.

Recommended Cache Pool Size

- GB

Minimum

—

Comfortable range

—

Nearest standard drive size

—

Mover Configuration

No Redundancy: Single SSD Cache Risk

A single-SSD cache pool has no redundancy. If it fails before the mover has moved your data to the array, that data can be lost. Consider keeping critical shares set to 'cache: No' so they write directly to the protected array, or mirror the cache pool with a second SSD.

ZFS adds checksumming and stronger data integrity features, but uses RAM for ARC. How much RAM it consumes depends on your workload, dataset size, and ARC settings. Whether ZFS is the right choice depends on your RAM headroom, workload, and comfort with added complexity. Unraid cache pool docs.

Shared Settings (from Tab 1) ▼ collapse

Daily ingest 50 GB/day

Write pattern Mixed

Mover schedule Daily

Filesystem BTRFS

These values are carried over from Tab 1. Update them there and re-run.

SSD TBW rating

TBW

Find this in your SSD datasheet. Common values: 250-2000 TBW.

SSD capacity

Estimated SSD Lifespan

- years

based on your TBW rating and estimated write patterns

Effective daily write

—

Write amplification

—

Your drive's endurance rating works out to —. DWPD (Drive Writes Per Day) expresses endurance as full-drive-writes per day over a 5-year warranty period — a figure below 0.3 DWPD is considered low for an always-on cache drive. Double-check the spec sheet, as some manufacturers list TBW per warranty period rather than drive lifetime. Understanding TBW and DWPD.

Methodology

Cache pool sizing adds two components: the write buffer (data accumulating before the Mover clears it) and fixed components that permanently reside on cache: Docker/container data, VM disk images, and appdata. The write buffer is sized at 2× daily ingest for the minimum and 3-4× for the comfortable range; if the mover runs daily or less frequently, an additional 1.5× is applied, and daily peak events add a further 20%. Fixed components are added to the write buffer total, then the sum is divided by 0.80 to ensure the pool never exceeds 80% capacity at peak usage (SSDs slow and wear faster above this threshold). The final figure is rounded up to the nearest standard drive size (250 GB, 500 GB, 1 TB, 2 TB, 4 TB).

SSD endurance is estimated by applying write amplification multipliers to daily ingest and comparing the annual write total against the drive's TBW rating. Write amplification reflects the extra I/O overhead from filesystem journaling, metadata writes, and small-file random patterns, ranging from 1.2× for large-file ZFS threshold-mover setups to 2.0× for small-file workloads. Monitor your cache drive's actual written bytes via SMART data in Unraid's dashboard (Main → Cache drive → SMART Data).

Last reviewed: 20 March 2026

Frequently Asked Questions

What is the Mover in Unraid and why does it matter for cache sizing?

The Mover is an Unraid process that transfers files from your cache pool to the main array on a schedule you define. Until the Mover runs, new writes sit on the cache. If the cache fills before the Mover clears it, writes either go directly to the slower array drives or stall entirely. Cache pool size must account for how much data accumulates between Mover runs.

Should I use threshold-based mover triggering or a schedule?

Threshold-based is better for most users. Set the Mover to trigger when the cache hits 70-80% full. Files stay on fast storage longer, you get fewer unnecessary write cycles, and you avoid the cache filling between scheduled runs. A common approach is to use the Mover Tuning plugin (free, available in Community Applications) to configure threshold-based triggering.

Does my cache pool protect against data loss?

Only if configured with redundancy. A mirror (2 SSDs) or RAIDZ/RAID1 pool can survive a single drive failure without data loss. A single-SSD cache pool has no redundancy, if it fails before the Mover has moved your data to the protected main array, that data can be lost.

What is the difference between BTRFS and ZFS for a cache pool?

Both filesystems work as Unraid cache pools. ZFS adds checksumming and stronger data integrity features, but uses RAM for its ARC cache, how much depends on workload, dataset size, and ARC settings. BTRFS is more RAM-efficient. Whether ZFS is the better choice depends on your available RAM headroom, workload, and tolerance for added complexity. See the Unraid cache pool docs for guidance.

My SSD is not listed, how do I find its TBW rating?

Search the manufacturer website or the product page for your specific SSD model. The TBW (Total Bytes Written) figure is listed in the specifications or endurance section of the datasheet. Common values range from 150 TBW for budget consumer drives to 2000+ TBW for enterprise or high-endurance models. Some manufacturers list TBW per warranty period rather than drive lifetime, so check the fine print.

How do I monitor my SSD's actual written bytes in Unraid?

In Unraid, go to Main, then select your cache drive, then click SMART Data. Look for attributes labelled Total Bytes Written or Host Writes. This shows the cumulative data written to the drive since manufacture. Compare this figure against your TBW rating annually to track remaining endurance.

AU SSD Cache Drive Pricing Reference (early 2026)

Unraid cache pools work best with SSDs rated for mixed-use or NAS workloads. Consumer drives work but have lower endurance (TBW ratings). AU retail prices from Mwave, PLE, Amazon AU.

Drive	Capacity	TBW	AU retail range	Notes
Samsung 870 EVO	1 TB	600 TBW	$120-$145	SATA, good all-round cache choice
Samsung 870 EVO	2 TB	1,200 TBW	$200-$235	SATA, value for larger cache pools
WD Red SA500	1 TB	500 TBW	$115-$140	SATA: NAS-rated, validated for Unraid
WD Red SN700 NVMe	1 TB	600 TBW	$130-$160	NVMe, higher throughput for media writes
WD Red SN700 NVMe	2 TB	1,300 TBW	$230-$270	NVMe, best option for high-write pools
Kingston KC600	1 TB	600 TBW	$100-$130	SATA, budget option, good endurance

Cache Pool Redundancy: AU Context

A single-SSD cache pool has no redundancy. If the cache SSD fails before Unraid's mover has moved data to the protected array, that data can be lost. Options:

Mirror cache pool (2× SSD): Add a second identical SSD. Unraid mirrors writes, one SSD can fail without data loss. Budget an additional $115-$160 for the mirror drive.
Shares set to cache: No: Keep critical shares writing directly to the protected array (slower but always protected).
Mover schedule: Run the mover more frequently (e.g., every 4 hours instead of nightly) to reduce the data-at-risk window.

ACL note: Consumer SSDs from AU retailers carry a 3-5 year warranty. For cache drives running high sustained writes (media ingest, VM workloads), NAS-rated SSDs like the WD Red SA500 or WD Red SN700 are validated for higher-endurance scenarios and are preferable despite the slight price premium.