Re: measuring swap partition speed
- Reply: void : "Re: measuring swap partition speed"
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Date: Thu, 21 Dec 2023 18:56:21 UTC
A bit weird that a simple dd is so slow. Just a quick thought. Are your partitions aligned properly? Is other IO going on on the same time? What does gstat say about %util, queue length and all the other stats while running the dd? Or "iostat -x -d 1". Could you try if another disk has the same issues? How is your disk connected? USB-to-SATA-adapter? Any output of dmesg? Regards, Ronald. Van: void <void@f-m.fm> Datum: donderdag, 21 december 2023 16:50 Aan: freebsd-fs@freebsd.org Onderwerp: Re: measuring swap partition speed > > On Wed, Dec 20, 2023 at 07:48:14PM -0800, Mark Millard wrote: > > ># swapoff /dev/label/growfs_swap > ># dd if=/dev/urandom of=/dev/da0s2b bs=8k count=250000 conv=sync status=progress > >^C478830592 bytes (479 MB, 457 MiB) transferred 22.001s, 22 MB/s > >60557+0 records in > >60556+0 records out > >496074752 bytes transferred in 22.790754 secs (21766491 bytes/sec) > > 22MB/s is usable, I think. In my context, I'd be satisfied with that. > My context differs from yours slightly in that yours is SSD and mine > is spinning rust. > > This is unusable: > # dd if=/dev/urandom of=/dev/da0p4 bs=8k count=250000 conv=sync status=progress > ^C11862016 bytes (12 MB, 11 MiB) transferred 40.063s, 296 kB/s > > because it's way too slow. Swap never gets fully reclaimed, > thrashing happens, loads of other followon effects happen. > The same partition formatted as ufs reports 113 MB/s. Multiple swap partitions > have been tested, then converted to ufs. Results are the same. > > There are no reported errors in smartctl. Long smartctl tests run monthly. > > 5 Reallocated_Sector_Ct PO--CK 100 100 050 - 0 > 9 Power_On_Hours -O--CK 001 001 000 - 48992 > 196 Reallocated_Event_Count -O--CK 100 100 000 - 0 > 197 Current_Pending_Sector -O--CK 100 100 000 - 0 > 198 Offline_Uncorrectable ----CK 100 100 000 - 0 > > I can't find any hardware problem here. Possible workarounds, bearing in mind I'm not versant in C so it's not like I can fix this myself in code: > > 1. swap as swapfile and not partition [a] > 2. swap as nfs [b] > 3. swapoff & swapon script running every minute [c] > 4. just turn all swap off and reboot after crashing (undesirable) > 5. use another OS that doesn't have this problem > > [a] not tried yet, and i hope it works. Legacy info suggests swap as partition is usually > faster than filesystem-based swap. But the reverse might be the case here. > > [b] also not tried. This, I imagine, would be filesystem only (I'm unsure a zfs volume can > be exported to look like a mountable partition to the client) > > [c] https://github.com/Freaky/swapflush.git - usually works but maybe i need to run it every minute instead of every five mins. For testing, this script was disabled. > > Any additional suggestions on how to overcome this problem gratefully received. > > -- > > > >