Contents
Comparing & synchronising folders
The core task of SynQaiPro always runs in two phases: first it analyses (compare only, change nothing), then it synchronises (carry out the proposed actions). That way you see exactly what will happen before anything is changed.
4.1 Step by step
- Choose the left and right folder (see chapter 2.1).
- Set the mode you want (→ ← ⇄ 🗑, see chapter 2.3).
- Click ⟳ Analyse — the comparison list fills up (status “Analysis running…”).
- Check the result and, if needed, tick or untick individual entries or adjust actions (chapter 5).
- Click ▶ Synchronise to carry out the actions.
4.2 The performance test before the first sync
Before the first synchronisation, SynQaiPro automatically determines the optimal number of parallel copy streams for the target drive (display “Performance test running…”). The result — for example “4× threads optimal (120.0 MB/s)” — is saved and reused for later runs. On slow media the program deliberately reduces to a single stream so as not to overload the disk (gentle mode).
Setting the copy streams yourself
Next to the performance display there is a small drop-down menu. Use it to override the automatic setting when it misjudges a drive:
| Setting | Meaning |
|---|---|
| A | Automatic (default) — hardware detection and the performance test determine the number |
| 1x | A single copy stream — the gentle mode for slow USB and SMR disks |
| 2x … 16x | A fixed number of parallel streams, regardless of the measurement |
As soon as a fixed setting is chosen, the performance test is greyed out — it would have no effect any more. A takes you back to automatic at any time. The setting applies per job and is saved with the project.
Why many streams slow a USB hard disk down
On SSDs, copying in parallel almost always brings more speed. On classic hard disks — and especially on external USB disks — the opposite is often true. Four things are behind this, and they reinforce one another:
1. There is only one write arm. Inside a hard disk, platters spin and a single movable arm writes on them. Copy four files at once and this one arm has to jump back and forth between four places on the platter without pause. It then spends more time jumping than writing. With a single stream it draws one long track in one go — the mode of operation a hard disk was built for. An SSD has no such arm; that is why the opposite rule applies there.
2. Windows reports “done” before it is done. To make copying feel fluid, Windows first takes the data into memory and reports completion to the program immediately — the actual write to disk happens in the background. As long as the disk keeps up, this buffer is an accelerator. If it cannot keep up, the buffer fills. And once it is full it no longer helps at all: from then on every further copy has to wait until the disk has really written. From the outside it looks as if everything ran briskly at first and then came to a standstill from one moment to the next. Exactly this pattern is the hallmark of an overloaded disk — not a steadily slow copy.
3. Many external disks write using shingled recording (SMR). On these, the data tracks overlap like tiles on a roof. Changing something in the middle therefore means the tracks above it have to be rewritten as well. So that this does not show in everyday use, such disks have a small fast area where they park new data first. Once that is full, the disk has to tidy up and reorganise — and while it does, its speed drops from well over a hundred to a few megabytes per second. Several streams fill that area correspondingly faster.
4. The USB bridge is a bottleneck. Every USB enclosure contains a small chip that translates between USB and the hard disk. It can only manage a limited number of requests at a time. Give it more and it works through them one after another — and in the worst case it stops responding for a while altogether. Then the time limit from section 4.5 expires and the affected files end up in the error list.
All told, a USB hard disk often achieves more with one stream than with four. That is precisely what the performance test measures, and precisely why SynQaiPro switches to gentle mode by itself on such drives.
4.3 Check tiers: how SynQaiPro detects differences
To keep the analysis fast and reliable, the program checks in tiers. The tier used is shown in the Check column:
| Tier | Method |
|---|---|
| Fast | Comparison by size and timestamp — very quick |
| Spot check | Sample-based content check at several points in the file |
| SHA-256 | Full checksum over the entire content — the safest but slowest tier |
The third tier (SHA-256) can be switched off deliberately — useful with very large amounts of data when size and timestamp are criteria enough for you and speed matters.
Using the SHA-256 button at the top
The upper toolbar holds the 🔍 SHA-256 switch for this. One click turns the deep check on or off for the current job. You can see the state at once:
- Green outline = ON: the tooltip reads “SHA-256 active — tier 3 in use”. Differences are confirmed by a full checksum.
- Dimmed/grey = OFF: the tooltip reads “SHA-256 disabled — tier 3 skipped (conservative: changed)”. The third tier is omitted.
4.4 Keeping an eye on disk space — before and after the sync
Below the comparison list sits the disk space line. It answers the most important question before every sync in real time: will this even fit on the target drive? For each side it shows three values:
| Value | Meaning |
|---|---|
| Need | How much additional space the selected files will take up on this side. If more files are deleted than copied, it reads Frees instead. |
| Currently free | The space currently free on the drive. |
| Free after sync | The space expected to be free once the sync has run. |
A ✔ in front of the line means “there is enough room”, a ⚠ warns of insufficient space (with the addition “— NOT SUFFICIENT”). If the space is enough, the line is green; if it gets tight, it turns red. Left and right side stand next to each other, separated by a vertical bar.
If you want to check before the analysis whether a particular folder fits on the other side, use the file tree context menu “Size analysis to the other side” — it writes its result (“✔ fits” or “⚠ does NOT fit (short by …)”) into the same disk space line (see chapter 6.5).
4.5 The synchronisation run
During the synchronisation, SynQaiPro shows the overall progress, an estimate of the remaining time and the current speed. In the list you see the live status per file: the currently active row (Active column), the transfer speed (Speed column) and, at the end, ✓ Done or ✗ Error.
The time display reads, for example, “Elapsed: 0:42 · Remaining: ~1:15”.
In addition, each row carries a thin bar along its bottom edge showing the state of that one file:
| Bar on the row edge | Meaning |
|---|---|
| mint green, moving | The file is being copied right now; the bar fills as it progresses. |
| red, flat | The file is ✗ Error — it was not transferred. The bar stays empty so that a failed copy does not look like a finished one. |
| no bar | Done (✓ Done) or not yet in turn. On success the green status arrow is enough. |
Keeping the running copies in view
When SynQaiPro works with several copy streams, several rows are active at once. They sit directly beneath one another in the list, because the files are processed in the order shown. So that this block does not wander off the bottom of the view while finished rows pile up above it, SynQaiPro scrolls along: the topmost running copy stays in the upper quarter. This is controlled by the anchor symbol ⚓ above the list:
- Orange = ON: the list follows the running copies.
- Neutral = OFF: the list stays put. You scroll yourself without the display pulling you back — handy when you want to look something up during the run.
The switch takes effect immediately and is harmless even in the middle of a running synchronisation — it only changes the display, not the copying. The setting applies to all jobs and survives a program restart.
When a drive stops responding
Occasionally a drive delivers nothing for a single file for minutes on end — because it keeps retrying a hard-to-read area, for instance. So that you are not left staring at a motionless bar and guessing, SynQaiPro says what is going on:
| When | Message in the log |
|---|---|
| after 8 seconds without progress | “⌛ Waiting for drive — file (12 s without response)” — the counter keeps running |
| as soon as it continues | “▶ Drive is responding again — file (paused 18 s)” |
| after a minute without response | “⌛ File stopped responding — skipped” — the file counts as an error |
The last case is the decisive one: a file that delivers nothing does not hold up the run. It is skipped, named in the log, and the sync carries on with the next one. At the end it appears in the error list — and because it remains uncopied, it shows up as pending again in the next analysis. A second run usually fetches it without trouble, because the drive is no longer under full load.
One error often drags others with it
Important when judging the error list: not every file marked red is damaged itself. A drive that gets stuck in one place often needs a while afterwards before it responds normally again. During that time the files being copied alongside run into the same time limit — and end up in the list as errors too, although there is nothing wrong with them. The more copy streams work at once, the more files are affected.
A block of red rows in immediate succession therefore usually means: one file threw the drive off its stride, the rest are bystanders. Which one it was is in the log — it is the first with the message “⌛ Waiting for drive”.
Retrying everything that failed with one click
The retry button exists for exactly this case. If a synchronisation left errors behind, a red ↻ with a number appears above the list at the end — the number of failed files. It sits right next to the anchor symbol. One click fetches all these files without you having to start a new analysis first. The button belongs to single-job operation: if you work with several jobs via the JobWorker, it does not appear (see chapter 3.3).
The button does not simply work through the list; it goes in two rounds:
| Round | What happens | Why |
|---|---|---|
| 1 | all failed files except the trigger file, with the normal number of copy streams | These are the bystanders. Usually nothing is wrong with them and they get through quickly. |
| Pause | around 20 seconds of rest for the drive | An overloaded disk reports back to the system immediately, but does not write normally for a while yet. The pause costs little and noticeably improves the odds. |
| 2 | the trigger file — on its own and with a single copy stream | It thus gets the best possible starting position: a settled drive and the full bandwidth to itself, without competition from other copies. |
The order is the real trick. If the trigger file came up at the same time as the others again, it would block the drive at the same moment as the first time — and drag the bystanders down with it once more. Last and alone, it has the best chances.
During the retry the list shows exactly the affected files and nothing else, with the usual progress bars. Cancelling is possible at any time, including during the pause between the rounds. Whatever did not get its turn stays noted as pending — so the red button does not disappear while anything is outstanding. At the end the log reports either “✔ Retry finished — no more errors” or how many files are still left.
4.6 Resuming cancelled copies
If a synchronisation is cancelled in the middle of a large file, SynQaiPro can save the part already copied and continue from that point on the next run instead of starting over. You recognise the switch by its colour:
- Orange = ON: cancelled copies of large files are saved and continued on the next sync.
- Neutral = OFF: a cancellation discards the copy state; the file starts from the beginning next time.
A resumable file carries a small resume badge in the list. The reset button (↺) discards saved partial copies.
Lifting the block deliberately
This block applies as long as the automatic setting determines the number of copy streams. If you know better — because the disk was merely in a bad state during the test, say — set the drop-down from section 4.2 from A to 2x or higher. That discards the automatic classification and the resume switch can be used again.
| Copy stream setting | Resume on a slow disk |
|---|---|
| A — automatic | blocked (gentle mode) |
| 1x — one stream | blocked — 1× is gentle mode |
| 2x … 16x | available |
4.7 Cancelling
✕ Cancel stops the analysis or synchronisation at any time. Files already finished are kept; the file in progress is ended cleanly (and saved for the next run if resume is active).
While the cancellation runs, a notice overlays the view (“Preparing to cancel …”). If it drags on, the text names the drive being waited for — for example “Cancelling — waiting for drive S:\ …”. You can therefore see that the program is working and what it is waiting on.