GlitchNZ

Thanks Jon, My main concern is about future scalability, so the fact that different raid versions can/will be supported give me hope. The main part of my question still stands though, does BTRFS do striping in RAID1? What exactly is it's version of RAID 1 and how does it differ from traditional RAID 1

I am about to upgrade to V6 from (Currently using 5.0.6) and I am very much looking forward to using the new Cache Pool Feature. I am about to purchase a number of Samsung Pro SSD's for an initial cache pool (and an 8TB HDD), and due to the price I want to make sure I get the most cost effective size/quantity. I may add more later and I need to make sure I have a solution that scales correctly by meeting the following requirements: Initial Cache will need at least 500GB usable space as I can write this much data in a single day Adding more drives should increase this space so that I can scale the pool overtime if needed The Cache will need to initially handle files ~300Gb in size The maximum file size should also be able to scale over time Looking through the current documentation it only says that it uses BTRFS's "unique twist on traditional RAID 1", not what this actually means. Normally RAID 1 is just mirroring, so if I needed 500GB usable space I would have to buy 1TB worth of hard drives. Also, normally RAID1 does not do striping so the maximum file size would be the about the same size as the smallest disk in the pool. If I assume standard RAID 1 then I would need 2x500GB drives to meet the above requirements. However, if BTRFS is genuinely different to RAID1 then maybe maybe the cheapest solution wold be something different (3x250GB for example). I would also be interested to know if the RAID system used can be changed - for example, to RAID 5 or RAID 10 so that I can use the version of raid most suited for my needs. I want to buy the SSD's (and an 8TB Seagate ) and preclear everything before I do the upgrade so that everything is all good to go. I'm looking forward to the combination of Super Fast SSD Cache with a stupidly cheap (and slow) 8TB parity, and I just want to make sure I get it right.

Just a note on this setup - The motherboard is a pain. Since I installed the SAS card I can not get it to keep its default boot order settings, which means right now I have to manually choose the boot device every time the system boots. Something about the SAS cards initialization process causes the motherboard to get confused and pick a new boot order at random - and it never chooses the USB. I am currently investigating new options. It is a shame because the CPU/mainboard pairing here is quite a cost-effective for a dedicated file server. Anyway, looking around the Unraid forums it seems like Gigabyte is not the most popular motherboard option for other reasons as well.

Its the second gen version which is PCIex8. The PCIex16 above was referring to the slot, but yes, it will only get PCIex8 performance.

System Mainboard: Gigabyte GA-F2A85X-D3H CPU: AMD A4-5300 APU with Radeon HD Graphics AuthenticAMD GNU/Linux RAM: 2X8GB Kingston HyperX Fury (Blue) DDR3 1333Mhz (Dual channel) PSU: Silverstone Strider Plus (850w) SST-ST85F-P - 80A single rail modular. PCIx16 slot: AOC-SAS2LP-MV8 SAS 2nd Gen expansion card (PCI Express 8x) Flash: Emtec 16GB USB 3.0 with Unraid 5.06 Professional Case: Silverstone ATX with 3x External fans, 9x3.5" bays. 4x5.25" with 2x Icydock 3-in-2 fan cooled cages, 6x2.5" cage. Hard Drives Physical Capacity Mainboard: 8 x SATA, 4xUSB3, 4xUSB2 SAS Card: 8xSATA Case: 15x3.5", 6x2.5" PSU Ideal: 20 PSU Max: 40 Currently Installed: Parity: 1x Western Digital Green 6TB Spare - ready to hotswap 1x Western Digital Green 6TB (3x precleared, installable in hotswappable Icydock bay) Data: 1x Seagate ST4000DM000 4TB 1x Western Digital Green 4TB 3x Western Digital Green 2TB 1x Seagate ST2000M001 2TB 1x Seagate ST1000M003 1TB 1x Hitachi HDT721010SLA360 1TB 1x Seagate ST3500320AS 500GB Currently 5 disks connected directly through SATA to the main board. 4 Disks connected via SAS breakout cable to SAS card (2 drives per channel)

This seriously looks like you have been sold a used drive. If this was the only preclear you have run then the results suggest it had reallocated sectors before you even ran the test. Like the previous posters, I would look at the number of power_on_hours (run the smart report from Unmenu if you have it) or run smartctl -a -d ata /dev/s?? from the command line. If the hours don't match your usage, not only would I send it back, but I would expect them to pay for shipping - they shouldn't be sending used drives. If the hours match, then RMA. Regardless of the above DO NOT use it in your array - it is on the verge of complete failure and will compromise your array protection.

In writing to the forum, I managed to accidentally stumble across the specific circumstances that cause this problem, although I can not think why these circumstances cause the problem, I can vouch that they do as I was able to replicate the results several times. It turns out that the slowness always occurred while another disk was going through the write phase of a preclear. After I wrote the first post, the temporary disk I was going to use to defragment the files had finished preclearing. When I went to get the data for the second post, I couldn't replicate the problem! On a hunch, I started another preclear last night and, during the pre-read I still could not replicate the problem. Only this evening when it was again doing a write phase could I reproduce the results and get the metrics above. While I had a file transferring at 50kb/s I cancelled the preclear and it shot back to 20MB/s within a few seconds. I cant imagine why writing zeros to a disk not in the array would affect transfers to disks in the array, and while I know the preclear script uses dd, I don't know enough about DD to see why this would happen. My best guess is that the preclear script somehow gets enough priority over the CPU/Main bus that it gets in the way of regular file transfers. Hope this info helps someone.

Some metrics (including syslog). Please note I have renamed the files in this post as I don't want to advertise filenames on a public forum. The number at the end of each dir/filename is the length in characters of the actual file/directory name. None of my files have any special characters other than spaces and brackets. Details scraped when a file is moving at a good pace: Terminal: root@Tower:/mnt/disk6# rsync -a --remove-source-files --progress SomeShare6/ /mnt/disk1/SomeShare6 sending incremental file list ASubDirectory19/AnotherSubdirectory14/ ASubDirectory19/AnotherSubdirectory14/AFile.14 3550511104 35% 12.10MB/s 0:08:36 Disk perf: Disk/Read/Write/Total sdb: 8247.51 KB/s 8247.51 KB/s 16495.01 KB/s (Target Disk) sde: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdd: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdc: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdf: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdg: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdh: 8247.51 KB/s 8247.51 KB/s 16495.01 KB/s (Parity Disk) sdj: 8183.63 KB/s 0.00 KB/s 8183.63 KB/s (Source disk) sdk: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdl: 0.00 KB/s 0.00 KB/s 0.00 KB/s total: 24678.64 KB/s 16495.01 KB/s 41173.65 KB/s Top: (from /usr/bin/top -b -n1) top - 18:06:49 up 4 days, 22:06, 1 user, load average: 1.36, 0.81, 0.37 Tasks: 118 total, 3 running, 115 sleeping, 0 stopped, 0 zombie Cpu(s): 8.7%us, 18.2%sy, 0.0%ni, 26.5%id, 43.8%wa, 0.0%hi, 2.8%si, 0.0%st Mem: 16051080k total, 13876924k used, 2174156k free, 253060k buffers Swap: 0k total, 0k used, 0k free, 13309592k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 6758 root 20 0 6464 788 312 R 18 0.0 0:41.95 rsync 6756 root 20 0 6448 1496 848 R 10 0.0 0:28.28 rsync 6760 root 20 0 0 0 0 S 10 0.0 0:07.58 flush-9:1 3241 root 20 0 0 0 0 S 4 0.0 529:24.67 unraidd 23109 root 20 0 0 0 0 S 2 0.0 0:11.46 kworker/0:0 1 root 20 0 828 284 240 S 0 0.0 0:11.15 init ... many more but probably not relevant. Syslog: No messages since start of transfer. Same metrics when rsync hits a slow file: Terminal root@Tower:/mnt/disk4# rsync -a --remove-source-files --progress SomeShare2/ /mnt/disk2/SomeShare2 sending incremental file list ASubDir25/ASubDir9/AFile.67 62947328 4% 93.22kB/s 4:26:42 Disk Perf Device Read Write Total sdb: 0.00 KB/s 0.00 KB/s 0.00 KB/s sde: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdd: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdc: 0.00 KB/s 0.00 KB/s 0.00 KB/s (Source) sdf: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdg: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdh: 0.00 KB/s 0.00 KB/s 0.00 KB/s (Parity) sdj: 0.00 KB/s 0.00 KB/s 0.00 KB/s sdk: 275.45 KB/s 0.00 KB/s 275.45 KB/s (Target) sdl: 0.00 KB/s 0.00 KB/s 0.00 KB/s total: 275.45 KB/s 0.00 KB/s 275.45 KB/s Top (from /usr/bin/top -b -n1) top - 18:05:09 up 5 days, 22:04, 1 user, load average: 3.12, 3.01, 2.39 Tasks: 120 total, 2 running, 118 sleeping, 0 stopped, 0 zombie Cpu(s): 7.5%us, 17.3%sy, 0.0%ni, 28.8%id, 43.6%wa, 0.0%hi, 2.8%si, 0.0%st Mem: 16051080k total, 11911860k used, 4139220k free, 532880k buffers Swap: 0k total, 0k used, 0k free, 11116256k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 5363 root 20 0 4112 2800 600 D 16 0.0 116:42.01 dd 413 root 20 0 0 0 0 S 8 0.0 386:35.39 kswapd0 5370 root 20 0 0 0 0 S 6 0.0 44:27.93 flush-8:128 14262 root 20 0 15676 1260 392 D 2 0.0 0:18.49 rsync 1 root 20 0 828 284 240 S 0 0.0 0:12.07 init 2 root 20 0 0 0 0 S 0 0.0 0:01.29 kthreadd 3 root 20 0 0 0 0 S 0 0.0 9:10.12 ksoftirqd/0 5 root 0 -20 0 0 0 S 0 0.0 0:00.00 kworker/0:0H 7 root 0 -20 0 0 0 S 0 0.0 0:00.00 kworker/u:0H 8 root RT 0 0 0 0 S 0 0.0 0:01.71 migration/0 9 root 20 0 0 0 0 S 0 0.0 0:00.00 rcu_bh 10 root 20 0 0 0 0 S 0 0.0 4:19.41 rcu_sched 11 root RT 0 0 0 0 S 0 0.0 0:01.72 migration/1 12 root 20 0 0 0 0 S 0 0.0 40:48.74 ksoftirqd/1 14 root 0 -20 0 0 0 S 0 0.0 0:00.00 kworker/1:0H 15 root 0 -20 0 0 0 S 0 0.0 0:00.00 khelper 16 root 20 0 0 0 0 S 0 0.0 0:00.01 kworker/u:1 167 root 20 0 0 0 0 S 0 0.0 0:00.05 bdi-default 169 root 0 -20 0 0 0 S 0 0.0 0:00.00 kblockd 276 root 0 -20 0 0 0 S 0 0.0 0:00.00 ata_sff 286 root 20 0 0 0 0 S 0 0.0 0:00.00 khubd 393 root 0 -20 0 0 0 S 0 0.0 0:00.00 rpciod 419 root 20 0 0 0 0 R 0 0.0 0:08.61 kworker/1:1 475 root 20 0 0 0 0 S 0 0.0 0:00.00 fsnotify_mark 495 root 0 -20 0 0 0 S 0 0.0 0:00.00 nfsiod 499 root 0 -20 0 0 0 S 0 0.0 0:00.00 cifsiod 514 root 0 -20 0 0 0 S 0 0.0 0:00.00 crypto 580 root 20 0 0 0 0 S 0 0.0 0:00.06 kworker/u:2 677 root 0 -20 0 0 0 S 0 0.0 0:00.00 deferwq 691 root 20 0 0 0 0 S 0 0.0 0:00.00 scsi_eh_0 692 root 20 0 0 0 0 S 0 0.0 0:00.10 usb-storage 731 root 16 -4 2460 1008 516 S 0 0.0 0:00.07 udevd 872 root 20 0 0 0 0 S 0 0.0 0:00.00 scsi_eh_1 873 root 20 0 0 0 0 S 0 0.0 0:00.00 scsi_eh_2 874 root 20 0 0 0 0 S 0 0.0 0:00.00 scsi_eh_3 875 root 20 0 0 0 0 S 0 0.0 0:00.00 scsi_eh_4 876 root 20 0 0 0 0 S 0 0.0 0:00.00 scsi_eh_5 877 root 20 0 0 0 0 S 0 0.0 0:00.00 scsi_eh_6 878 root 20 0 0 0 0 S 0 0.0 0:00.00 scsi_eh_7 879 root 20 0 0 0 0 S 0 0.0 0:00.00 scsi_eh_8 886 root 20 0 0 0 0 S 0 0.0 0:00.00 scsi_eh_9 1005 root 0 -20 0 0 0 S 0 0.0 0:00.00 scsi_wq_9 1006 root 0 -20 0 0 0 S 0 0.0 19:38.67 kworker/0:1H 1007 root 0 -20 0 0 0 S 0 0.0 21:48.05 kworker/1:1H 1103 root 20 0 2072 768 524 S 0 0.0 0:00.95 syslogd 1107 root 20 0 1856 384 320 S 0 0.0 0:00.03 klogd 1137 root 20 0 2044 552 444 S 0 0.0 0:00.01 dhcpcd 1161 bin 20 0 2852 492 404 S 0 0.0 0:00.00 rpc.portmap 1168 root 20 0 2108 796 664 S 0 0.0 0:00.00 rpc.statd 1185 root 20 0 1900 556 488 S 0 0.0 0:00.01 inetd 1192 root 20 0 8196 2924 2240 S 0 0.0 0:29.11 ntpd 1200 root 20 0 1864 636 536 S 0 0.0 0:00.00 acpid 1210 messageb 20 0 3368 616 464 S 0 0.0 0:00.00 dbus-daemon 1215 root 20 0 1908 592 508 S 0 0.0 0:01.24 crond 1217 daemon 20 0 1900 296 220 S 0 0.0 0:00.00 atd 1297 root 20 0 3152 1168 812 S 0 0.0 0:01.18 screen 1298 root 20 0 4368 1736 1260 S 0 0.0 0:00.02 bash 1299 root 20 0 5028 2356 1180 S 0 0.0 0:32.40 preclear_disk.s 1568 root 20 0 6736 1500 1172 S 0 0.0 1:54.72 emhttp 1576 root 20 0 2644 496 320 S 0 0.0 0:00.00 uu 1577 root 20 0 1840 520 456 S 0 0.0 0:00.00 logger 1583 root 20 0 8764 7560 936 S 0 0.0 3:46.21 awk 1587 root 0 -20 0 0 0 S 0 0.0 0:00.00 md 1588 root 20 0 0 0 0 S 0 0.0 203:12.27 mdrecoveryd 1591 root 20 0 0 0 0 S 0 0.0 0:00.00 spinupd 1592 root 20 0 0 0 0 S 0 0.0 0:00.00 spinupd 1594 root 20 0 0 0 0 S 0 0.0 0:00.00 spinupd 1596 root 20 0 0 0 0 S 0 0.0 0:00.00 spinupd 1597 root 20 0 0 0 0 S 0 0.0 0:00.00 spinupd 1600 root 20 0 0 0 0 S 0 0.0 0:00.00 spinupd 1601 root 20 0 0 0 0 S 0 0.0 0:00.00 spinupd 1602 root 20 0 0 0 0 S 0 0.0 0:00.00 spinupd 1603 root 20 0 0 0 0 S 0 0.0 0:00.00 spinupd 1605 root 20 0 0 0 0 S 0 0.0 0:00.00 spinupd 2601 root 20 0 10004 1908 1360 S 0 0.0 0:34.02 nmbd 2620 root 20 0 16532 3836 3104 S 0 0.0 0:01.90 smbd 2636 root 20 0 16532 1932 1200 S 0 0.0 0:01.08 smbd 2661 root 20 0 0 0 0 S 0 0.0 0:00.00 lockd 2662 root 20 0 0 0 0 S 0 0.0 0:00.00 nfsd 2663 root 20 0 0 0 0 S 0 0.0 0:00.00 nfsd 2664 root 20 0 0 0 0 S 0 0.0 0:00.00 nfsd 2665 root 20 0 0 0 0 S 0 0.0 0:00.00 nfsd 2666 root 20 0 0 0 0 S 0 0.0 0:00.00 nfsd 2667 root 20 0 0 0 0 S 0 0.0 0:00.00 nfsd 2668 root 20 0 0 0 0 S 0 0.0 0:00.00 nfsd 2669 root 20 0 0 0 0 S 0 0.0 0:00.00 nfsd 2685 root 20 0 2272 176 0 S 0 0.0 0:00.00 rpc.mountd 2705 avahi 20 0 3052 1596 1352 S 0 0.0 0:02.65 avahi-daemon 2708 avahi 20 0 2912 396 212 S 0 0.0 0:00.00 avahi-daemon 2730 root 20 0 2036 520 428 S 0 0.0 0:00.00 avahi-dnsconfd 3241 root 20 0 0 0 0 S 0 0.0 583:07.86 unraidd 3254 root 18 -2 2456 976 468 S 0 0.0 0:00.06 udevd 3255 root 18 -2 2456 808 312 S 0 0.0 0:00.00 udevd 3678 root 0 -20 0 0 0 S 0 0.0 0:00.00 reiserfs 5500 root 20 0 53504 3512 604 S 0 0.0 9:08.56 shfs 6048 root 20 0 1856 532 472 S 0 0.0 0:00.00 agetty 6049 root 20 0 1856 536 472 S 0 0.0 0:00.00 agetty 6050 root 20 0 1856 528 472 S 0 0.0 0:00.00 agetty 6051 root 20 0 1856 532 472 S 0 0.0 0:00.00 agetty 6052 root 20 0 1856 536 472 S 0 0.0 0:00.00 agetty 6053 root 20 0 1856 536 472 S 0 0.0 0:00.00 agetty 13119 root 20 0 0 0 0 S 0 0.0 0:01.39 kworker/0:0 13351 root 20 0 6876 1952 1496 S 0 0.0 0:00.17 in.telnetd 13352 root 20 0 4352 1784 1312 S 0 0.0 0:00.03 bash 13477 root 20 0 0 0 0 D 0 0.0 0:00.52 kworker/1:2 13503 root 20 0 0 0 0 S 0 0.0 0:00.17 flush-9:2 14256 root 20 0 15756 1888 852 S 0 0.0 0:01.74 rsync 14257 root 20 0 15052 1212 620 S 0 0.0 0:00.00 rsync 16934 root 20 0 0 0 0 S 0 0.0 0:00.00 kworker/1:0 17541 root 20 0 0 0 0 S 0 0.0 0:00.00 kworker/0:1 21222 root 20 0 0 0 0 S 0 0.0 0:00.00 kworker/1:3 21863 root 20 0 0 0 0 S 0 0.0 0:00.00 kworker/0:2 23450 root 20 0 22656 6304 5168 S 0 0.0 4:09.22 smbd 23624 root 20 0 1892 580 432 S 0 0.0 0:00.00 sleep 23650 root 20 0 2324 948 768 S 0 0.0 0:00.00 gawk 23653 root 20 0 2608 916 796 S 0 0.0 0:00.00 sh 23654 root 20 0 2488 960 728 R 0 0.0 0:00.00 top 24366 root 20 0 22412 4656 3824 S 0 0.0 0:11.82 smbd 26597 root 20 0 16652 3168 2420 S 0 0.0 0:00.75 smbd 27473 root 20 0 22656 5400 4460 S 0 0.0 0:35.23 smbd Syslog No Messages during, or for preceding 9 hours. Looking at the metrics, slow writing to sdk may be indicative of a problem, so in anticipation of your next question, below is the smart status report for that disk: Statistics for /dev/sdk WDC_WD40EZRX-00SPEB0_WD-WCC4E0216764 smartctl -a -d ata /dev/sdk smartctl 6.2 2013-07-26 r3841 [i686-linux-3.9.11p-unRAID] (local build) Copyright (C) 2002-13, Bruce Allen, Christian Franke, www.smartmontools.org === START OF INFORMATION SECTION === Device Model: WDC WD40EZRX-00SPEB0 Serial Number: WD-WCC4E0216764 LU WWN Device Id: 5 0014ee 2b3c4bf85 Firmware Version: 80.00A80 User Capacity: 4,000,787,030,016 bytes [4.00 TB] Sector Sizes: 512 bytes logical, 4096 bytes physical Rotation Rate: 5400 rpm Device is: Not in smartctl database [for details use: -P showall] ATA Version is: ACS-2 (minor revision not indicated) SATA Version is: SATA 3.0, 6.0 Gb/s (current: 6.0 Gb/s) Local Time is: Mon Dec 8 18:13:32 2014 NZDT 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: (0x82) Offline data collection activity was completed without error. 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: (53940) 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: ( 539) minutes. Conveyance self-test routine recommended polling time: ( 5) minutes. SCT capabilities: (0x7035) SCT Status 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 200 200 051 Pre-fail Always - 0 3 Spin_Up_Time 0x0027 217 172 021 Pre-fail Always - 6125 4 Start_Stop_Count 0x0032 098 098 000 Old_age Always - 2123 5 Reallocated_Sector_Ct 0x0033 200 200 140 Pre-fail Always - 0 7 Seek_Error_Rate 0x002e 200 200 000 Old_age Always - 0 9 Power_On_Hours 0x0032 089 089 000 Old_age Always - 8109 10 Spin_Retry_Count 0x0032 100 100 000 Old_age Always - 0 11 Calibration_Retry_Count 0x0032 100 253 000 Old_age Always - 0 12 Power_Cycle_Count 0x0032 100 100 000 Old_age Always - 36 192 Power-Off_Retract_Count 0x0032 200 200 000 Old_age Always - 21 193 Load_Cycle_Count 0x0032 190 190 000 Old_age Always - 30663 194 Temperature_Celsius 0x0022 124 110 000 Old_age Always - 28 196 Reallocated_Event_Count 0x0032 200 200 000 Old_age Always - 0 197 Current_Pending_Sector 0x0032 200 200 000 Old_age Always - 1 198 Offline_Uncorrectable 0x0030 200 200 000 Old_age Offline - 1 199 UDMA_CRC_Error_Count 0x0032 200 200 000 Old_age Always - 1 200 Multi_Zone_Error_Rate 0x0008 200 200 000 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% 7938 - # 2 Extended offline Completed without error 00% 7768 - # 3 Extended offline Interrupted (host reset) 60% 7755 - # 4 Short offline Completed without error 00% 7750 - 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. This disk has shown pending correctable in the past, and I ran a preclear cycle on it to check if it would reallocate or not. The preclear appeared to fix this, and I don't think a single pending correctable would explain the current issue.

***Edit*** This issues arises when trying to transfer files between disks in an array while the preclear script is doing the write phase on another disk. My advice: don't expect to do large transfers while preclearing a disk. In my case my CPU is low powered (see below) so this may not be an issue for gruntier systems. ***End Edit*** I am currently trying to tidy up the distribution of shares on my array. I have been running the array for some years and some shares have become quite randomly distributed across various drives, which in the event of a failure would be a nightmare to deal with. I have been mostly using midnight commander to move files from one disk to another to consolidate shares on just a few drives (instead of across 5 or more), which is mostly working quite well, however some files seem to cause problems. At seemingly random intervals, MC will transfer a file extremely slowly (less than 1KB/sec instead of the usual 30-70 MB/s). When this happens, accessing the array over the network also slows down (e.g. the web gui is slow to load and accessing other shares slows down as well). The issue appears to affect specific files, so files 1,2,4 and 5 in a directory transfer fine, but file 3 is slow. This behavior occurs for the same files regardless of whether I use MC, rsync or just standard mv command. The behavior is not drive specific, I have experienced this issue transferring from and to various drives. The behavior may be linked to very long file paths - I note the problem seems most likely to occur with files that have a long path and name, although I have many files that fit this category so I can't be certain. I am about to test if fragmentation could be the culprit by transferring file to and from a temporary disk I have set up, although my understanding of reiserfs and current hard drive speeds suggest that this shouldn't be an issue. Some possibly useful info: uname -a: Linux Tower 3.9.11p-unRAID #5 SMP Sat Dec 21 19:37:06 PST 2013 i686 AMD A4-5300 APU with Radeon(tm) HD Graphics AuthenticAMD GNU/Linux free: total used free shared buffers cached Mem: 16051080 8504316 7546764 0 241692 7980628 -/+ buffers/cache: 281996 15769084 Swap: 0 0 0 When mc hits a 'slow' file, top shows an impressive increase in load (up to 6+), however there does not seem to be any process using a lot of CPU or Memory and the CPU and Memory usage remains low Gigabit Ethernet 9 disks from 500GB up to 4TB, 6TB parity drive. Most disks are 2TB or larger and less than 3 years old. Recent SMART tests on all disks have passed, and all disks were correctly precleared 3 times before insertion into the array. Approx 30% free space spread fairly evenly across the array. Any suggestions as to what maybe causing this odd behavior and how to resolve it would be more than welcome. As it is, the low speed on these files makes them essentially unmovable (moving a 6GB file at 800 bytes a second would take 237 Years.