Too slow · Reviewed October 14, 2026 · Prices updated 1 hour ago

Why Is My NAS So Slow?

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Back up before you repair. If the data on this system exists nowhere else, copy what matters to another device first, while the drives still read.

Quick answer

Check the pool, the client computer and the network path before you suspect the drives. Synology says to repair a degraded pool first and to test from another PC, and both Synology and QNAP list cable, link speed and MTU checks that need no new drive. A drive needs replacing only when one drive stands out in the makers' drive checks.

Reviewed October 14, 2026

Check your situation

Is any storage pool degraded, or is a repair, drive addition or RAID type change running?

Repair the pool or let the task finish. Repair a degraded pool first, using the steps for your NAS on the degraded pool page below. If a repair, a drive addition or a RAID type change is running, let it finish, then test the transfer again. Nothing needs buying for the speed problem itself.

The computer is the bottleneck, not the NAS. Synology says the computer's CPU and disk should not be overloaded during the transfer. Synology says to temporarily disable or remove firewall, anti-virus and other security software on the computer, and to keep its network card driver up to date. QNAP lists a slow computer as one cause of slow writes. QNAP suggests testing the computer's own disk, for example with a USB external drive, to rule out a local storage bottleneck that can look like a NAS problem. Nothing needs buying for the NAS.

Fix the network path. Synology says to use a wired network instead of Wi-Fi. Synology suggests connecting the PC and the NAS directly with an Ethernet cable. If the rate rises, the router, switch or another device in between might have issues. Check the link speed the NAS reports. Synology lists 1000 Mbps for a 1GbE port and 10000 Mbps for a 10GbE port. QNAP says that if the speed is lower than expected, check the cable type, the switch port and the network card's negotiation settings first. QNAP says a 10GbE network card that has negotiated down to 1GbE or lower caps throughput at about 117 MB/s. QNAP also says half-duplex negotiation can cut throughput sharply; try a different cable or switch port. Cable grade: Synology says the cable should be CAT5/e or above, not bent or degraded, and to try another cable. QNAP's example is that a 1000Mbps network needs a CAT6 cable. QNAP says receive or transmit errors, drops or overruns on a network interface can point to a cable, SFP or switch port problem. MTU: Synology says the default is 1500, and that if you change it, every device that reaches the NAS must support and use the same value. QNAP's quick test is to set MTU to 1500 on all devices and test again. If speed improves, jumbo frames are likely set up wrong; they must be on for the NAS, the switch port and the computer's network card. To see which ports your model has, compare with the site's NAS list below. Nothing in the site's tables is needed for this fix.

Wait, reschedule or stop the task. QNAP says scheduled pool scrubbing and scheduled backup jobs can make transfer speeds drop sharply while they run. If the slowdown comes at set times, check those schedules first. QNAP says a scrub reads every block on every disk and can cut transfer performance by 50% or more while it runs. That figure is QNAP's. QNAP says a backup job that runs during user file transfers competes with them for disk access. On Synology, if CPU use is extremely high, find the service or package behind it in DSM Resource Monitor > Task Manager and stop it for a while. QNAP says to disable unused apps in App Center to free resources. Nothing needs buying.

Free space, drop encryption or test without the cache. Synology says that if volume usage exceeds 90%, try to free up space. Synology gives no other usage figure. QNAP says encryption slows transfers. Use a shared folder and volume that are not encrypted, and turn off SMB encryption if it is on. QNAP says a degraded SSD cache can throttle disk access: check Storage & Snapshots > Cache Acceleration. For slow reads, QNAP lists disabling SSD cache acceleration as a setting to try. QNAP warns this may lower performance for a while on workloads that rely on the cache, and suggests doing it in a maintenance window. Nothing needs buying.

Replace the one drive that stands out. On Synology, watch DSM Resource Monitor > Performance > Disk during a transfer. Look for a drive with a much higher utilization rate than the others in the array. Synology says that if one drive is in bad status or its utilization rate is extremely high, replace it with a new, healthy drive. On QNAP, run the Sequential Read Test in Storage & Snapshots on every disk and compare the results. QNAP says to replace a disk with low speed, giving less than 80 MB/s as its example, and to note the slot and model of a disk much slower than the rest. QNAP also says to check S.M.A.R.T. health when disk throughput looks abnormal. Synology says the drives should be on its Products Compatibility List, and the array should not mix PMR and SMR drives. Check a model number with the Is My Drive SMR? tool on this page: it answers CMR, SMR, not stated by the maker, or not in our records, and names the maker document. Synology also says the type and number of drives and the RAID configuration affect performance. The table below lists only new NAS and enterprise drives whose maker confirms CMR, with live Amazon.com prices. Make sure the pool is healthy before you swap a drive.

Work it out for your hardware

Try: , , , ,

The rules this tool applies, with their sources, are on its own page: Is My Drive SMR?.

Safe steps

These actions can lose data. Do none of them until a copy exists elsewhere:

Synology says to repair a degraded pool first.
Interrupting a repair, a drive addition or a RAID type change to get speed back. Synology says to wait for these activities to complete.

Change one thing at a time and test again after each change. Write down your network, MTU, bonding and switch settings before you change them.^[4]
QNAP's network speed test gives about 940 Mbps (about 117 MB/s) on 1GbE and about 9.4 Gbps (about 1.17 GB/s) on 10GbE.^[4]
QNAP's reading of that test: if it is also low, the network path is the bottleneck. If it is normal, the physical network is likely fine and the problem is in the file service layer.^[4]

What to buy, if anything

Answer the questions under "Check your situation" and this section narrows to what your case calls for. Until then every table is shown, each with the case it is for.

CMR NAS drives to replace one slow or unhealthy drive

Why this is here: Shown only for the outcome where one drive is the cause: Synology says to replace a drive that is in bad status or has an extremely high utilization rate compared with the others, and QNAP says to replace a disk with low speed in its sequential read test. It is also the CMR replacement when the array mixes PMR and SMR drives, which Synology says to avoid. A client, network, cable, MTU, background-task, full-volume or settings cause needs no purchase. New 3.5-inch SATA NAS and enterprise hard drives whose maker confirms CMR recording, with today's Amazon.com price per TB.

Price per

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30 products

Product	Capacity	Price	$ / TB	Type	Prime	Buy
DC HC550 16TB 512MB SATA Ultra SE NP3	16 TB	$589.45	$36.84	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Seagate IronWolf 14TB NAS Internal Hard Drive HDD – CMR 3.5 Inch SATA 256MB Cache for RAID Network Attached Storage – Frustration Free Packaging (ST14000VN0008)	14 TB	$525.00	$37.50	NAS HDD · SATACMR	-	Buy on Amazon
TOSHIBA N300 Internal Hard Drive 22 Tb 7200 RPM 512 Mb 3.5", W129161818 (Tb 7200 RPM 512 Mb 3.5 Serial Ata Iii)	22 TB	$830.82	$37.76	NAS HDD · SATACMR	-	Buy on Amazon
Toshiba - HDWG82AXZSTB - Toshiba N300 Pro HDWG82AXZSTB 20 TB Hard Drive - 3.5 Internal - SATA (SATA/600) - Conventional	20 TB	$766.99	$38.35	NAS HDD · SATACMR	-	Buy on Amazon
Toshiba MG Series Enterprise 12TB 3.5’’ SATA 6Gbit/s Internal HDD 7200RPM 550TB/year 24/7 Operation. MG07ACA12TE	12 TB	$469.99	$39.17	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Seagate IronWolf Pro, 16 TB, Enterprise NAS Internal HDD –CMR 3.5 Inch, SATA 6 Gb/s, 7,200 RPM, 256 MB Cache for RAID Network Attached Storage (ST16000NT001)	16 TB	$629.99	$39.37	NAS HDD · SATACMR	-	Buy on Amazon
Seagate Enterprise 3.5" 18000 GB 7200 RPM 18 TB 3.5" 7200 RPM SATA ST18000NM00J	18 TB	$712.00	$39.56	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Seagate Enterprise Capacity \| ST10000NM0016 \| 10TB 7200 RPM SATA 6.0Gb/s 256MB Cache Hyperscale 512e 3.5" Hard Disk Drives	10 TB	$399.95	$39.99	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Western Digital WUH721414ALE6L4 14TB Ultrastar DC HC530 SATA HDD - 7200 RPM Class, SATA 6 Gb/s, 512MB Cache, 3.5"	14 TB	$581.00	$41.50	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Seagate 20TB Exos Enterprise Hard Drive \| SATA (ST20000NM002H) \| Enterprise nearline HDD for AI, cloud & data centers. Always-on performance, helium sealed, 2.5M-hr MTBF. 5-Year Warranty	20 TB	$829.99	$41.50	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Toshiba - HDWG81GXZSTB - Toshiba N300 Pro HDWG81GXZSTB 16 TB Hard Drive - 3.5 Internal - SATA (SATA/600) - Conventional	16 TB	$685.50	$42.84	NAS HDD · SATACMR	-	Buy on Amazon
Seagate 14TB HDD Exos X14 7200 RPM 512e/4Kn SATA 6Gb/s 256MB Cache 3.5-Inch Enterprise Hard Drive (ST14000NM0018)	14 TB	$600.00	$42.86	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
HGST WD Ultrastar DC HC510 10TB 7200 RPM SATA 6Gb/s 3.5" Helium Platform Enterprise Hard Disk Drive - HUH721010ALE604 (0F27606)	10 TB	$429.00	$42.90	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Seagate Exos X18 Enterprise Class, 16TB, Enterprise Internal Hard Drive, SATA, 3,5" 6Gbit/s, 128MB Cache (ST16000NM000J)	16 TB	$686.91	$42.93	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Seagate IronWolf 10TB NAS Internal Hard Drive, 3.5" SATA 6Gb/s, 7200 RPM, CMR, RAID Optimized, IronWolf Health Management – for NAS Systems (ST10000VNZ00)	10 TB	$432.99	$43.30	NAS HDD · SATACMR	-	Buy on Amazon
Western Digital 22TB WD Red Pro NAS Internal Hard Drive HDD - 7200 RPM, SATA 6 Gb/s, CMR, 512 MB Cache, 3.5" - WD221KFGXSold by Amazon	22 TB	$958.90	$43.59	NAS HDD · SATACMR	Prime	Buy on Amazon
Seagate Exos X10 ST10000NM0126 10TB 7200 RPM SATA 6Gb/s 512e 256MB 3.5in Enterprise Hard Drive	10 TB	$439.99	$44.00	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Western Digital 20TB WD Red Pro NAS Internal Hard Drive HDD - 7200 RPM, SATA 6 Gb/s, CMR, 512 MB Cache, 3.5" - WD202KFGXSold by Amazon	20 TB	$881.68	$44.08	NAS HDD · SATACMR	Prime	Buy on Amazon
Western Digital 18TB WD Red Pro NAS Internal Hard Drive HDD - 7200 RPM, SATA 6 Gb/s, CMR, 512 MB Cache, 3.5" - WD181KFGX	18 TB	$794.99	$44.17	NAS HDD · SATACMR	-	Buy on Amazon
Western Digital 24TB WD Red Pro NAS Internal Hard Drive HDD, 7200 RPM, SATA 6 Gb/s, CMR, 512 MB Cache, 3.5" - WD241KFGXSold by Amazon	24 TB	$1,059.99	$44.17	NAS HDD · SATACMR	Prime	Buy on Amazon
Seagate IronWolf Pro 14TB NAS Internal Hard Drive HDD – CMR 3.5 Inch SATA 6Gb/s 256MB Cache for RAID Network Attached Storage, Data Recovery Service – Frustration Free Packaging (ST14000NEZ008)	14 TB	$619.99	$44.29	NAS HDD · SATACMR	-	Buy on Amazon
Seagate IronWolf 16TB NAS Internal Hard Drive HDD – CMR 3.5 Inch SATA 6GB/S 7200 RPM 256MB Cache for Raid Network Attached Storage, with Rescue Service (ST16000VN001)	16 TB	$711.00	$44.44	NAS HDD · SATACMR	-	Buy on Amazon
Seagate IronWolf Pro ST12000NE0008 12 TB Hard Drive - 512E Format - SATA 600-3.5" Drive - Internal - 7200RPM - 256 MB Buffer - Hot Pluggable	12 TB	$534.99	$44.58	NAS HDD · SATACMR	-	Buy on Amazon
Seagate Exos X14 ST12000NM0008 12 TB Hard Drive - 3.5" Internal - SATA (SATA/600)	12 TB	$535.68	$44.64	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Western Digital 16TB WD Red Pro NAS Internal Hard Drive HDD - 7200 RPM, SATA 6 Gb/s, CMR, 512 MB Cache, 3.5" - WD161KFGXSold by Amazon	16 TB	$714.99	$44.69	NAS HDD · SATACMR	Prime	Buy on Amazon
Western Digital 12TB WD Red Plus NAS Internal Hard Drive HDD - 7200 RPM, SATA 6 GB/s, CMR, 512 MB Cache, 3.5" - WD120EFGX	12 TB	$538.88	$44.91	NAS HDD · SATACMR	-	Buy on Amazon
Western Digital 12TB WD Red Pro NAS Internal Hard Drive HDD - 7200 RPM, SATA 6 Gb/s, CMR, 512 MB Cache, 3.5" - WD122KFBXSold by Amazon	12 TB	$539.16	$44.93	NAS HDD · SATACMR	Prime	Buy on Amazon
Seagate IronWolf 10Tb NAS Internal Hard Drive HDD – 3.5 Inch SATA 6GB/S 7200 RPM 256MB Cache for Raid Network Attached Storage (ST10000VN0004)	10 TB	$449.99	$45.00	NAS HDD · SATACMR	-	Buy on Amazon
HGST - WD Ultrastar DC HC520 HDD \| HUH721212ALE600 \| 12TB 7.2K SATA 6Gb/s 256MB Cache 3.5-Inch Helium Data Center Internal Hard Disk Drive	12 TB	$541.45	$45.12	Enterprise HDD · SATACMREnterprise	-	Buy on Amazon
Western Digital 10TB WD Red Plus NAS Internal Hard Drive HDD - 7200 RPM, SATA 6 GB/s, CMR, 512 MB Cache, 3.5" - WD100EFGXSold by Amazon	10 TB	$455.75	$45.58	NAS HDD · SATACMR	Prime	Buy on Amazon

Sources

Synology Knowledge Center: What can I do with low data transfer rate? checked 2026-10-14
QNAP FAQ: What should I do if I'm experiencing Slow File Transfer issue over Ethernet/thunderbolt/USB? checked 2026-10-14
QNAP tutorial: What to do if my NAS data transfer rate is slow? checked 2026-10-14
QNAP FAQ: How do I troubleshoot it if my NAS transfer speeds dropped dramatically? checked 2026-10-14

Facts on this page were reviewed on October 14, 2026. Prices and stock are from Amazon.com as of October 14, 2026.