Constant disc activity after reboot

[luismartin]

On which TOS version did you observe this constant disc activity?

Only when TOS7 was installed. Not for TOS5 or 6.

[MikeZhang]

Our lab. will manage to reproduce this issue and find solution asap

[MikeZhang]

We have TOS7 released officially, please update and keep observing if the issue persists
viewtopic.php?t=10179
If yes, please click below link to book remote session, we will check for you remoteyl.
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[MikeZhang]

We have TOS7 released officially, please update and keep observing if the issue persists
for TOS7 beta user ---viewtopic.php?t=10179
for TOS6.0.794 user ---viewtopic.php?t=10183
If yes, please click below link to book remote session, we will check for you remoteyl.
https://salesiq.zohopublic.com/signatur ... 97d0be8892

[magnus4ever]

Regarding the issue you encountered, here is a detailed explanation:

Persistent hard drive read/write activity following system reboot

When the cache mode is set to Write-Back Mode, data written to the NAS is first stored at high speed in the M.2 SSD. Data blocks that have been written to the SSD but not yet synchronized back to the mechanical hard drive are referred to as "Dirty Blocks" in storage technology.

If I understand this correctly, this means that cached files are not synced to the drive and remain in the cache? Does the cache only dump the files on the HDD when the SSD capacity is full?

My understanding of the feature was that once data is written on the SSD, its immeadiately synced to the HDD, which apparently is not the case. Otherwise the system wouldnt freak out upon reboot and detect all those unsynced files.

Would a smaller cache drive help with this issue or at least limit the busy time after reboot?

Just checked with my F4-424 (TOS 6.0.794, Cache in Read/Write Mode, 512GB M.2): Drives busy after reboot for ~45mins, activity immeadiately seizes once "Dirty Blocks" have reached 0%.

[EriChan]

First of all, thank you for sharing your test data.

Regarding your concerns, here is a detailed explanation and suggestion:

1. Does the cache only dump files when the SSD is full?
No, it doesn't wait until it's full.
In Read-Write Mode, when you write data to the NAS, the system acknowledges the write as "complete" the moment it hits the high-speed SSD (which is why your write speeds are so fast).

However, the system does not wait for the SSD to fill up to start moving data to the HDDs. Instead, it constantly and quietly trickles data from the SSD to the HDDs in the background when the system is relatively idle.

2. Why does the system "freak out" upon reboot then?
If it syncs continuously, why are there so many unsynced files after a reboot? There are two main reasons:

• Accumulated Cache: If you did heavy write operations shortly before the reboot, the background flusher might not have had enough "idle time" to finish syncing everything.

• Boot-up Flush & Integrity Check: When TOS boots up, its storage daemon prioritizes data integrity. To prevent any potential file system corruption, the system aggressively spins up the HDDs to flush all remaining "Dirty Blocks" from the SSD journal down to the platters as quickly as possible. This is why you see frantic 100% disk activity right after booting up.

Note: If your goal is for data to be immediately and simultaneously written to both the SSD and HDD, you should switch to Balanced Mode (which acts closer to Write-Through). However, please note that this will lower your sequential write speeds down to the HDD's native limit.

3. Would a smaller cache drive limit the busy time?
Technically yes, but it’s a double-edged sword.
A smaller SSD (e.g., 128GB or 256GB) has a lower maximum capacity, meaning the absolute volume of 95% dirty blocks is much smaller than that of a 1TB or 2TB drive. Therefore, the worst-case flushing time after a reboot would indeed be shorter.

However, we do not recommend downgrading for this reason. A smaller cache drive means a much lower cache hit rate, and it will trigger the system's active recycling mechanism much faster during daily use, which can hurt overall performance.

Recommendation:
Your 512GB SSD taking ~45 minutes to completely sync after a boot is entirely normal behavior for a Write-Back cache ensuring your data is safely committed to the hard drives.

If the noise and disk activity after a reboot bother you, the best approaches are:

• Minimize unnecessary reboots.

• Switch to Balanced Mode if you prefer immediate syncing and an instantaneous quiet boot, at the expense of peak write performance.

[magnus4ever]

Wow, thank you for this detailes response, really appreciate the activity of the team in this forum!

Will try changing over to balanced mode as my WiFi speed is the limiting factor anyway when accessing the NAS.