Date: Thu, 13 Apr 2017 11:08:23 +0100 From: tech-lists <tech-lists@zyxst.net> To: freebsd-questions@freebsd.org Subject: Re: hopefully simple query regarding dd Message-ID: <33df8ac0-3d45-2945-fd4f-f4068ce60f8c@zyxst.net> In-Reply-To: <20170413103601.ae71e4fa9a2b5d9b024a71fc@sohara.org> References: <7ed0944d-56d0-fc10-629b-b90067f48651@zyxst.net> <20170413103601.ae71e4fa9a2b5d9b024a71fc@sohara.org>
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On 13/04/2017 10:36, Steve O'Hara-Smith wrote: > It should be safe and work, assuming that what you want to do is > read and rewrite every block. You should probably think very hard about > what you want it to do in the case of read and/or write errors. > > I'm not sure why you'd want to do it though, discs are not > particularly volatile storage even on timescales of years. > > Of course if it ever gets a read error that passes the CRC > (aka silent corruption) it will cement the error in stone for you by > writing it back. > > If you are really concerned about long term data retention then I > suggest ZFS with plenty of redundancy (at least two drives redundancy) and a > regular scrub. Hi, The context is this: old netbook, slow cpu (boo!) low power (yay!) .. was thinking of making it a server on either the local or external LAN. AMD C-70 APU with Radeon(tm) HD Graphics (998.20-MHz K8-class CPU) real memory = 4294967296 (4096 MB) avail memory = 3781300224 (3606 MB) <WDC WD3200BPVT-22JJ5T0 01.01A01> ATA8-ACS SATA 2.x device ada0: Serial Number WD-WX51A3312496 ada0: 300.000MB/s transfers (SATA 2.x, UDMA6, PIO 8192bytes) ada0: Command Queueing enabled ada0: 305245MB (625142448 512 byte sectors) ada0: quirks=0x1<4K> Brand new freebsd-12 install as of yesterday. I think ZFS might just kill it though. Before installing, I ran a dd if=/dev/zero of=/dev/ada0 bs=1m conv=noerror from the shell option in the installer because if there were blocks giving errors, I wanted to re-map them somewhere safe. After installing, the first thing I did was to install and run smartd to see where I was with the disk. I knew previously the disk was likely to have errors. Here's the relevant stats: 9 Power_On_Hours -O--CK 085 085 000 - 11379 191 G-Sense_Error_Rate -O--CK 001 001 000 - 759 5 Reallocated_Sector_Ct PO--CK 183 183 140 - 143 197 Current_Pending_Sector -O--CK 001 001 000 - 65216 198 Offline_Uncorrectable ----CK 100 253 000 - 0 196 Reallocated_Event_Count -O--CK 196 196 000 - 4 194 Temperature_Celsius -O---K 104 089 000 - 39 Basically, I want that Current_Pending_Sector number to go to 0. I guess if it doesn't, then it's either replace the disk or it's time to dispose of the netbook. Right now it's rebuilding 12 with witness/invariants disabled, so I can't really do the dd thing I earlier asked about right now. I just needed to know if it could be run without having to reinstall. thanks, -- J.
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