> On Jul 30, 2026, at 1:04 PM, Alexander V. Makartsev <[email protected]> wrote: > > On 7/30/26 18:17, Casey Deccio wrote: >>> On Jul 29, 2026, at 5:28 PM, Andy Smith <[email protected]> >>> <mailto:[email protected]> wrote: >>> >>> ... >>> If it does occur when /home is mounted, then it is the disks in the RAID >>> setup or the RAID setup itself. Does each individual disk perform >>> anomalously? >>> >>> "fio" is a good tool,to carry out performance testing of storage >>> devices. Have a look what the random 4k read and write I/O is like in >>> terms of IOPS, and the sequential disk transfer rate in MB/s for reads >>> or writes. You can try that on the array and then break the array and >>> try it on each individual disk. Obviously this is destructive to the >>> data. >>> >>> If the performance is as expected on a per-disk basis but terrible only >>> with RAID, it may be time to post to the linux-raid mailing list as this >>> is unlikely to be a Debian-specific issue. I would then also be checking >>> if it happens in other RAID configurations like RAID-1. >>> >>> 150 IOPS of random reads (not coming from RAM) is reasonable for a >>> single 7.2kRPM SATA disk. You could expect 2-3x this from a RAID-5 of >>> three identical disks. >>> >>> Write IOPS is a bit more difficult to guess and will depend on whether >>> you have disabled the write cache in the drives themselves. Due to the >>> RAID-5 write penalty (read-modify-write) you may expect only 50-70% of a >>> single disk's IOPS for random writes. >> Thanks for that very helpful information. I've run fio on the >> still-assembled array, and here's what I get for read/write: >> >> read: IOPS=237 >> write: IOPS=79 >> >> I'm not sure exactly what to make of that... > I might add insult to the injury, but are you sure you need RAID-5 if it > consists of just 3 drives? > Usually around 30% per drive's capacity will be sacrificed to hold error > correction data for the array, > so maybe it will be much better to use 2 drives in RAID-1 (Mirror) > configuration, if you need decent write performance. > Third drive could be used as spare device for the array, or a separate > storage without redundancy.
Great ideas. I originally did RAID5 because I wasn't sure how many drives I wanted in the array, and I wondered if I might grow the array at some point. But I'll consider RAID 1 if I settle on three drives. Thanks, Casey
