John_M

Thanks Brian. I've noticed that smartctl returns a lot of unknown attributes when used with SSDs but that for HDDs they are generally well defined. It would be useful to fill in this gap. I've asked WD Support for information and I'll report back with anything interesting. Meanwhile, I'm still pre-clearing. It's 72% of the way through the zeroing phase and it's fast: the Reds (no slouches themselves) are a long way behind at 35%, 33% and 33%, respectively. I'm using your version of the script (many thanks for that, btw) to speed up the verifying phase so perhaps by Friday it will have finished. I'll be back.

Well, I traded hard disks with my colleague. I felt a bit bad at the cost difference and offered him some cash in addition to meet him half way, but he's happy that he got what he needs and he realises I'm taking something of a risk, so he refused the money. I put the 6 TB Re disk and three 6 TB WD Reds in a new HP Microserver Gen8 that I'd bought recently to build a small unRAID server for my brother but the thing is so cute I'm keeping it for myself and I'll buy another one for him! It's straight out of the box with Celeron 1610T processor and 4 GB of ECC RAM. These beauties are so inexpensive (about the same price as one of the disks) and so full of possibilities I might yet get a third one to experiment with! Anyway, I know from other threads that they'll run unRAID just fine provided you set the embedded storage controller to AHCI mode. I also enabled the drive write cache option, which is off by default. Here's a snippet from the syslog where the first two disks are detected, showing the 4Kn nature of /dev/sdb and the 512e nature of /dev/sdc for comparison. Note that the latter has exactly eight times as many 512-byte logical sectors as the former has 4096-byte sectors: Jan 12 18:23:14 Northolt kernel: ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300) Jan 12 18:23:14 Northolt kernel: ata1.00: ATA-10: WDC WD6001FXYZ-01SUYB1, WD-WX61D65744ES, ER43, max UDMA/133 Jan 12 18:23:14 Northolt kernel: ata1.00: 1465130646 sectors, multi 0: LBA48 NCQ (depth 31/32), AA Jan 12 18:23:14 Northolt kernel: ata1.00: configured for UDMA/133 Jan 12 18:23:14 Northolt kernel: scsi 1:0:0:0: Direct-Access ATA WDC WD6001FXYZ-0 ER43 PQ: 0 ANSI: 5 Jan 12 18:23:14 Northolt kernel: sd 1:0:0:0: Attached scsi generic sg1 type 0 Jan 12 18:23:14 Northolt kernel: sd 1:0:0:0: [sdb] 1465130646 4096-byte logical blocks: (5.86 TB/5.45 TiB) Jan 12 18:23:14 Northolt kernel: sd 1:0:0:0: [sdb] Write Protect is off Jan 12 18:23:14 Northolt kernel: sd 1:0:0:0: [sdb] Mode Sense: 00 3a 00 00 Jan 12 18:23:14 Northolt kernel: sd 1:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA Jan 12 18:23:14 Northolt kernel: sd 1:0:0:0: [sdb] 1465130646 4096-byte logical blocks: (5.86 TB/5.45 TiB) Jan 12 18:23:14 Northolt kernel: sd 1:0:0:0: [sdb] 1465130646 4096-byte logical blocks: (5.86 TB/5.45 TiB) Jan 12 18:23:14 Northolt kernel: sd 1:0:0:0: [sdb] Attached SCSI disk Jan 12 18:23:14 Northolt kernel: ata2: SATA link up 6.0 Gbps (SStatus 133 SControl 300) Jan 12 18:23:14 Northolt kernel: ata2.00: ATA-9: WDC WD60EFRX-68MYMN1, WD-WX21D45C7NKU, 82.00A82, max UDMA/133 Jan 12 18:23:14 Northolt kernel: ata2.00: 11721045168 sectors, multi 0: LBA48 NCQ (depth 31/32), AA Jan 12 18:23:14 Northolt kernel: ata2.00: configured for UDMA/133 Jan 12 18:23:14 Northolt kernel: scsi 2:0:0:0: Direct-Access ATA WDC WD60EFRX-68M 0A82 PQ: 0 ANSI: 5 Jan 12 18:23:14 Northolt kernel: sd 2:0:0:0: [sdc] 11721045168 512-byte logical blocks: (6.00 TB/5.45 TiB) Jan 12 18:23:14 Northolt kernel: sd 2:0:0:0: Attached scsi generic sg2 type 0 Jan 12 18:23:14 Northolt kernel: sd 2:0:0:0: [sdc] 4096-byte physical blocks Jan 12 18:23:14 Northolt kernel: sd 2:0:0:0: [sdc] Write Protect is off Jan 12 18:23:14 Northolt kernel: sd 2:0:0:0: [sdc] Mode Sense: 00 3a 00 00 Jan 12 18:23:14 Northolt kernel: sd 2:0:0:0: [sdc] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA Jan 12 18:23:14 Northolt kernel: sd 2:0:0:0: [sdc] Attached SCSI disk After successfully booting, I checked the SMART status of all drives and ran the short self-test. Here's the initial SMART report for the Re disc. Does anyone know what attribute 16 refers to? smartctl 6.2 2013-07-26 r3841 [x86_64-linux-4.1.13-unRAID] (local build) Copyright (C) 2002-13, Bruce Allen, Christian Franke, www.smartmontools.org === START OF INFORMATION SECTION === Device Model: WDC WD6001FXYZ-01SUYB1 Serial Number: WD-WX61D65744ES LU WWN Device Id: 5 0014ee 004180f60 Firmware Version: ER43 User Capacity: 6,001,175,126,016 bytes [6.00 TB] Sector Size: 4096 bytes logical/physical Rotation Rate: 7200 rpm Device is: Not in smartctl database [for details use: -P showall] ATA Version is: ACS-3 (unknown minor revision code: 0x006d) SATA Version is: SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s) Local Time is: Tue Jan 12 20:41:03 2016 GMT SMART support is: Available - device has SMART capability. SMART support is: Enabled === START OF READ SMART DATA SECTION === SMART overall-health self-assessment test result: PASSED General SMART Values: Offline data collection status: (0x80) Offline data collection activity was never started. Auto Offline Data Collection: Enabled. Self-test execution status: ( 0) The previous self-test routine completed without error or no self-test has ever been run. Total time to complete Offline data collection: ( 0) seconds. Offline data collection capabilities: (0x7b) SMART execute Offline immediate. Auto Offline data collection on/off support. Suspend Offline collection upon new command. Offline surface scan supported. Self-test supported. Conveyance Self-test supported. Selective Self-test supported. SMART capabilities: (0x0003) Saves SMART data before entering power-saving mode. Supports SMART auto save timer. Error logging capability: (0x01) Error logging supported. General Purpose Logging supported. Short self-test routine recommended polling time: ( 2) minutes. Extended self-test routine recommended polling time: ( 575) minutes. Conveyance self-test routine recommended polling time: ( 6) minutes. SCT capabilities: (0x003d) SCT Status supported. SCT Error Recovery Control supported. SCT Feature Control supported. SCT Data Table supported. SMART Attributes Data Structure revision number: 16 Vendor Specific SMART Attributes with Thresholds: ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 1 Raw_Read_Error_Rate 0x002f 200 100 051 Pre-fail Always - 0 3 Spin_Up_Time 0x0027 100 100 021 Pre-fail Always - 0 4 Start_Stop_Count 0x0032 100 100 000 Old_age Always - 3 5 Reallocated_Sector_Ct 0x0033 200 200 140 Pre-fail Always - 0 7 Seek_Error_Rate 0x002e 100 100 000 Old_age Always - 0 9 Power_On_Hours 0x0032 100 100 000 Old_age Always - 2 10 Spin_Retry_Count 0x0032 100 100 000 Old_age Always - 0 11 Calibration_Retry_Count 0x0032 100 100 000 Old_age Always - 0 12 Power_Cycle_Count 0x0032 100 100 000 Old_age Always - 3 16 Unknown_Attribute 0x0022 000 200 000 Old_age Always - 309738010 183 Runtime_Bad_Block 0x0032 100 100 000 Old_age Always - 0 192 Power-Off_Retract_Count 0x0032 200 100 000 Old_age Always - 1 193 Load_Cycle_Count 0x0032 200 100 000 Old_age Always - 1 194 Temperature_Celsius 0x0022 113 113 000 Old_age Always - 39 196 Reallocated_Event_Count 0x0032 200 100 000 Old_age Always - 0 197 Current_Pending_Sector 0x0032 200 100 000 Old_age Always - 0 198 Offline_Uncorrectable 0x0030 100 100 000 Old_age Offline - 0 199 UDMA_CRC_Error_Count 0x0032 200 200 000 Old_age Always - 0 200 Multi_Zone_Error_Rate 0x0008 100 100 000 Old_age Offline - 0 SMART Error Log Version: 1 No Errors Logged SMART Self-test log structure revision number 1 Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error # 1 Short offline Completed without error 00% 0 - SMART Selective self-test log data structure revision number 1 SPAN MIN_LBA MAX_LBA CURRENT_TEST_STATUS 1 0 0 Not_testing 2 0 0 Not_testing 3 0 0 Not_testing 4 0 0 Not_testing 5 0 0 Not_testing Selective self-test flags (0x0): After scanning selected spans, do NOT read-scan remainder of disk. If Selective self-test is pending on power-up, resume after 0 minute delay. It all looks very good so far. My next step with new disks is to pre-clear them. I know that opinions differ, but I'm not one who pre-clears a disk to death. I do (1) a SMART short self-test, followed by (2) a single pre-clear pass, followed by (3) a SMART long self-test. If it fails (1) I reject the disk. If it fails (2) I repeat once and reject if it fails on the second pass. If it passes (3) I put the disk into service. All four disks are currently on the pre-read phase of pre-clear. After 3.5 hours the Re is 34% through the pre-read, while the Red next to it is at 28%. So the Re is fast, having the advantage of high density platters similar to those used in the Red plus a faster spin speed. I'm also happy to say that it passed the 12.5% (one-eighth) point without smashing the actuator into its end-stop, so I'm confident that the pre-clear script handles 4Kn disks properly. It's also running a little warmer than the Reds, but not worryingly so. I'll report back when the pre-clears have finished. If all is still good I'll run the SMART long self-test on all four drives (polling time is 575 minutes for the Re compared with 692 for the Red, which is nearly two hours faster) and then I'll run the diskspeed script before assigning the disks to an array.

Since these error messages appear in the plugin's own log, not the general syslog, I suspect most users never see them. But for me at least they are a major problem and for now I've had to uninstall the plugin. I'd like to ask others to check their /var/log/unassigned.devices.log please. I have not been able to update from the 2015.09.19 because of this issue and some other outstanding issues that prevent me from mounting and using my backup drives. gfjardim doesn't seem to be active right now, so I wouldn't expect an update to the plugin. Ah, I see. So it is a general problem with the current version. I was beginning to think it was peculiar to my setup and that of a few others. Is there any way I could install the older version? Is it archived somewhere?

Since these error messages appear in the plugin's own log, not the general syslog, I suspect most users never see them. But for me at least they are a major problem and for now I've had to uninstall the plugin. I'd like to ask others to check their /var/log/unassigned.devices.log please.

Please report back with your findings. Too many threads just peter out, leaving the issue seemingly unresolved and causing frustration to others who search through them looking for a solution to a similar problem.

No comments? Is nobody interested? I've decided to get the drive and experiment with it. It might prove to be an expensive mistake or it might simply just work. I'm more hopeful of success than I would be using Windows. Either way, it should be educational. I've done a search of the boards but I haven't found anything about 4k native disks and unRAID.

Interesting. I notice that the edge connectors of PCI and PCIe cards seldom sit squarely in their sockets. I usually end up adjusting the screws and bending the metal bracket to try to counteract the tendency for it to lift the card out of its socket. It's probably down to the cheap cases I sometimes use!

Jan 10 18:20:50 Lapulapu kernel: xor: automatically using best checksumming function: Jan 10 18:20:50 Lapulapu kernel: r8169 0000:04:00.0 eth0: jumbo features [frames: 9200 bytes, tx checksumming: ko] Both are being flagged as Minor issues. Is it the word "checksumming" that's causing the false positive, for some reason?

From your syslog it all starts to go wrong at 20:54:13, when your AOC-SASLP-MV8 loses contact with the disk on its port ata9, which was earlier identified at 19:38:51 as being disk WDC_WD1002FAEX-00Z3A0_WD-WCATRC210436 (/dev/sdd). I've had a similar experience with the same controller and (a different) AMD chipset that I mention briefly here. The things that I tried replacing as I was troubleshooting are listed in order: SAS breakout cable (easy to change), power supply (a bad PSU or power cabling can cause all kinds of difficult to diagnose problems), hard disks (obvious, really!). Despite all being fine from a SMART point of view, I ended up retiring the old disks and replacing them with new, bigger ones. This fixed the problem. I'm able to pre-clear four disks at the same time on the AOC-SASLP-MV8 (I haven't tried any more) but I agree that it's generally safer to use the motherboard ports.

I agree with everyone above but, to answer the OP's question, you'd have to copy all the files from your original flash drive to the new empty one, name it UNRAID, make it bootable by running the script as you did on your original flash drive, then boot your server from it and register it in order to get a new trial key, then install the new trial key because registration keys, whether trial, basic, plus or pro, are tied to the physical flash drive. I use 8 GB flash drives because smaller ones are quite difficult to find these days but they are overkill and a 2 GB one, say, would be more than adequate. I prefer the very small Verbatim nano flash drives that are sometimes labelled Store 'n' Go. They stick out of the socket little more than an eighth of an inch and are equally ideal for plugging into the back of a server or into a motherboard socket.

Hi. I've got the opportunity to acquire a WD6001FXYZ (6 TB Western Digital Re) in exchange for a WD60EFRX (6 TB Western Digital Red) and I wondered if it would make a good parity disk alongside regular Reds as data disks. It's a 7200 RPM enterprise SATA III disk and it uses the 4Kn advanced format, not 512e. It's brand new, was bought in error by a colleague and it normally costs almost double what I'd have to "pay" for it. So, is it a bargain or should I avoid it?

I've got the same mass of error messages in my unassigned.devices.log (they accumulate at a rate of several per second) but my UI is as responsive as it was before I installed the plugin. I'm running unRAID 6.1.6 and the current version of the plugin (2015.11.18). Did you ever resolve this issue? Sat Jan 9 2:34:43 GMT 2016: PHP Warning: set_error_handler() expects the argument () to be a valid callback in /usr/local/emhttp/plugins/dynamix/include/DefaultPageLayout.php(276) : eval()'d code on line 550 Sat Jan 9 2:34:45 GMT 2016: PHP Warning: set_error_handler() expects the argument () to be a valid callback in /usr/local/emhttp/plugins/unassigned.devices/UnassignedDevices.php on line 428 Sat Jan 9 2:34:45 GMT 2016: PHP Warning: set_error_handler() expects the argument () to be a valid callback in /usr/local/emhttp/plugins/unassigned.devices/UnassignedDevices.php on line 428 Sat Jan 9 2:34:45 GMT 2016: PHP Warning: set_error_handler() expects the argument () to be a valid callback in /usr/local/emhttp/plugins/unassigned.devices/UnassignedDevices.php on line 428 Sat Jan 9 2:34:45 GMT 2016: PHP Warning: set_error_handler() expects the argument () to be a valid callback in /usr/local/emhttp/plugins/unassigned.devices/UnassignedDevices.php on line 428 Line 428 of the UnassignedDevices.php file reads set_error_handler($ori_error_handler); but I don't understand the code as grepping the file for ori_error_handler returns no other instance of the string. So unless ori_error_handler is defined globally somewhere else, then set_error_handler() is being passed a null argument - hence the error message. Is anyone else seeing this. Maybe the author might be able to comment? Update: I've installed the plugin on my other unRAID server and I'm getting the same error messages in its unnassigned.devices.log Update: In less than 11 hours the log file has grown to over 4 MB. I'm going to have to uninstall the plugin. Update: Uninstalled. Rebooted. Re-installed. Same problem - same error message repeated over and over. Has anyone else seen this? How do I fix it? Uninstalled and rebooted. I'll live without it for the time being. Update: Exactly the same on two different unRAID servers.

Check your parity drive's settings (Main|Parity) and make sure that the Spin down delay hasn't inadvertently been set to Never. I had a data drive that would never spin down and I discovered this setting had somehow been changed from Default. It may not be the case for you but it's an easy thing to check.

There's something I may have misunderstood, so I'm running my tests again, regarding my .DS_Store problem. Can I just check something, please? Under the File Integrity Control tab, am I right in thinking that the Check button initiates a check of the files against their exported checksums and not against the checksums stored in the extended attributes and it isn't a manual equivalent of the scheduled daily/weekly check, which does use the extended attributes? If I am right, then what is the result of clicking the Check button without ever clicking the Export button? Could that explain the "bunker: warning: is missing" messages in my syslog? I've stopped adding files to my shares for the time being and I've run Build again, and then Export. My disks now have both Initial Build and Initial Export green checks. I'm running Check at the moment and hope to see no errors this time. Nice plugin, btw Many thanks. EDIT: The manual check has completed with no errors reported. I'll use the server as normal and see if any errors are reported after the scheduled check on Sunday.

I'm getting checksum errors reported on Macintosh .DS_Store files. It seems possible that when I add files to a folder on my unRAID share using the OS X Finder the .DS_Store file within that folder is being updated but its checksum isn't, which results in the file corruption messages. unRAID file corruption: 07-01-2016 09:49 Notice [LAPULAPU] - bunker check command Found 6 files with BLAKE2 hash key corruption Syslog snippet: Jan 7 03:52:47 Lapulapu bunker: warning: is missing Jan 7 03:52:48 Lapulapu bunker: warning: is missing Jan 7 03:58:18 Lapulapu bunker: warning: is missing Jan 7 03:59:04 Lapulapu bunker: warning: is missing Jan 7 04:24:40 Lapulapu bunker: warning: is missing Jan 7 04:25:03 Lapulapu bunker: warning: is missing Jan 7 05:48:36 Lapulapu bunker: error: BLAKE2 hash key mismatch, /mnt/disk1/L_Public/.DS_Store is corrupted Jan 7 05:48:36 Lapulapu bunker: warning: is missing Jan 7 05:48:36 Lapulapu bunker: warning: is missing Jan 7 05:52:11 Lapulapu bunker: error: BLAKE2 hash key mismatch, /mnt/disk1/L_Public/Shared Videos/.DS_Store is corrupted Jan 7 05:53:22 Lapulapu bunker: error: BLAKE2 hash key mismatch, /mnt/disk1/L_Public/Shared Videos/DVD Rips/.DS_Store is corrupted Jan 7 06:53:48 Lapulapu bunker: error: BLAKE2 hash key mismatch, /mnt/disk1/L_Public/Shared Videos/DVD Rips/3 MKVs/.DS_Store is corrupted Jan 7 07:08:10 Lapulapu kernel: mdcmd (68): spindown 0 Jan 7 07:08:11 Lapulapu kernel: mdcmd (69): spindown 2 Jan 7 08:12:44 Lapulapu bunker: error: BLAKE2 hash key mismatch, /mnt/disk1/L_Public/Shared Videos/EyeTV Archive/.DS_Store is corrupted Jan 7 09:15:00 Lapulapu emhttp: cmd: /usr/local/emhttp/plugins/dynamix.plugin.manager/scripts/plugin checkall Jan 7 09:45:16 Lapulapu bunker: error: BLAKE2 hash key mismatch, /mnt/disk1/L_Public/Shared Videos/MakeMKV/.DS_Store is corrupted Jan 7 09:49:16 Lapulapu bunker: checked 49978 files from source /boot/config/plugins/dynamix.file.integrity/disk1.export.hash. Found: 0 mismatches (updated), 6 corruptions. Duration: 06:36:46 Average speed: 118. MB/s Perhaps the lines containing "is missing" are a clue. Is there a way of telling the plugin to exclude .DS_Store files?

I'm slightly puzzled by your choice of hard disks. Your post mentions four but your wishlist only shows three. I personally find it odd that you've chosen three different models and two different capacities. If I wanted to start out with just 6 TB of capacity (as your 3 TB WD Red Pro and your 3 TB HGST NAS, plus 4 TB WD Re parity disk will give you) I'd simply buy a pair of 6 TB WD Reds (WD60EFRX), one for parity and one for data. Then, as my needs grew I'd add more knowing that there's plenty of room for expansion and a large enough parity drive. I can't really comment on your other hardware as I don't understand your VM requirements.

I only thing I can add to the virtualisation discussion is that I can see that a Windows 7 VM would need a graphics card but I'm surprised by the implication that pfSense needs one too. Regarding your question about the BR120i controller, make sure it's set to AHCI mode and it will work just fine with unRAID. Note that there's a fifth SATA port available in addition to the four for the hard disk bays. It's intended for use with a DVD drive in the optical bay so if you forego that drive you can use it for your SSD and release a precious bay for a fourth hard disk. The slight downside to this is that this port (along with the two rightmost HDD bays) runs at 3 Gb/s SATA II. The two leftmost HDD bays run at 6 Gb/s SATA III so you have to make a choice. Personally, I'd go for maximum HDD bays (4 x 6 TB) and slower SSD but then I only use my SSD as an unRAID cache - I don't use VMs, which is why I chose the (almost insanely) cheaper Celeron powered model with 4 GB of ECC RAM. There's a single PCIe x16 slot. Not having any VMs, the slot is currently empty. If I was to add a card in the future it would likely be an eSATA controller to further extend the capacity externally.

I can't say categorically that it will work because I haven't tested it but since the drive enclosure has a separate eSATA connector for each hard disk (others I've seen use a single eSATA connector and a port multiplier) I don't see why it shouldn't. The card you've chosen has two SATA and two eSATA ports and the controller chip is the Marvell 88SE9235, which I believe is supported - the hardware compatibility list is somewhat outdated so it would be worth searching the forums for problems anyone has encountered with that particular device. Bear in mind that it needs a PCIe x2 or bigger slot. If that's a problem and you only have a x1 slot free there's an alternative card in the IO Crest (aka SYBA) family, the SI-PEX40065, which also has two SATA and two eSATA ports but uses the 88SE9215 chip. Since you presumably plan to use only the eSATA ports (I assume your reason for this exercise is that you have no further space for internal expansion) then the reduced bandwidth between motherboard and card shouldn't be an issue. If you go ahead, please report back your success or otherwise.

I downloaded the latest version and it is indeed fixed. Many thanks.

I have an AOC-SASLP-MV8 which produces false positives, the second and third lines below being highlighted as errors, presumably by the presence of the word "error". Is there a way to filter this out, please? Jan 5 00:31:16 Lapulapu kernel: sas: Enter sas_scsi_recover_host busy: 0 failed: 0 Jan 5 00:31:16 Lapulapu kernel: sas: ata9: end_device-1:0: dev error handler Jan 5 00:31:16 Lapulapu kernel: sas: ata10: end_device-1:1: dev error handler Thanks for making the highlight colours customisable. Some of the default pastel shades look too similar to my eyes.

OK. Thank you. That certainly sounds like the safe way to do it, so that's what I'll do.

My main unRAID server has a Pro registration key and I'm happy with it. My experimental unRAID server has a Plus key and after recently expanding it it now has the maximum 12 disks but I still have two unused SATA ports and I'd like to add a two SSD cache pool. The obvious thing to do would be to purchase a Pro upgrade for my Plus registration key. However, I've decided that I'd prefer to buy a new Pro key and use that instead and then repurpose my Plus key to build a new server for my brother. My first question is, how do I best move the current configuration from the old Plus key to the new unconfigured but bootable Pro key? My second question is, how do I best delete the configuration from my old Plus key so that I can start again on new hardware? I'm sure there are lots of ways to achieve my aim but I'm looking for a safe and efficient method. Many thanks.

It might be a bad SATA cable. See how the controller keeps resetting the link and after several attempts at communicating at 3 Gb/s it tries at 1.5 Gb/s a couple of times before giving up. I guess it could equally well be a bad controller port or bad drive electronics (damaged by static, perhaps?) but simply reseating the cable (as you did when you replaced the drive) might well have fixed it. I've come to the conclusion that SATA connectors are not the best designed in the world and the general stiffness of the standard red cables doesn't help.

Very nice. It makes searching through a log so much easier. One of the colours used (mid grey) doesn't appear in the legend.

I recently pre-cleared four disks simultaneously that were attached to the same "half" of an AOC-SASLP-MV8. The first three completed within minutes of each other; the fourth took about an hour longer, so I think that fourth disk probably saturated the card. A more modern card (such as your AOC-SAS2LP-MV8) with more PCIe lanes can probably support more simultaneous pre-clears without saturating, so six should not be an unreasonable number to try. Not sure what you mean by "Can Preclear truly multi-task?" You can run multiple instances of the pre-clear script, certainly. It's the Linux kernel that schedules the pre-emptive multi-tasking.