Re: Disk I/O slowness
Casey Deccio <[email protected]> Thu, 30 Jul 2026 14:49:04 -0600
| Newsgroups | gmane.linux.debian.user |
|---|---|
| Message-ID | <[email protected]> |
--Apple-Mail=_E5E0242D-E2CA-4760-9BCF-28826199D6F8 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Jul 30, 2026, at 1:04=E2=80=AFPM, Alexander V. Makartsev = <[email protected]> wrote: >=20 > On 7/30/26 18:17, Casey Deccio wrote: >>> On Jul 29, 2026, at 5:28=E2=80=AFPM, Andy Smith = <[email protected]> <mailto:[email protected]> wrote: >>>=20 >>> ... >>> 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? >>>=20 >>> "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. >>>=20 >>> 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. >>>=20 >>> 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. >>>=20 >>> 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: >>=20 >> read: IOPS=3D237 >> write: IOPS=3D79 >>=20 >> 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,=20 > 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= --Apple-Mail=_E5E0242D-E2CA-4760-9BCF-28826199D6F8 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8 <html aria-label=3D"message body"><head><meta http-equiv=3D"content-type" = content=3D"text/html; charset=3Dutf-8"></head><body = style=3D"overflow-wrap: break-word; -webkit-nbsp-mode: space; = line-break: after-white-space;"><br><div><blockquote type=3D"cite"><div>On= Jul 30, 2026, at 1:04=E2=80=AFPM, Alexander V. Makartsev = <[email protected]> wrote:</div><br = class=3D"Apple-interchange-newline"><div> =20 <meta http-equiv=3D"Content-Type" content=3D"text/html; = charset=3DUTF-8"> =20 <div> <div class=3D"moz-cite-prefix">On 7/30/26 18:17, Casey Deccio = wrote:<br> </div> <blockquote type=3D"cite" = cite=3D"mid:[email protected]"> <pre wrap=3D"" class=3D"moz-quote-pre"></pre> <blockquote type=3D"cite"> <pre wrap=3D"" class=3D"moz-quote-pre">On Jul 29, 2026, at = 5:28=E2=80=AFPM, Andy Smith <a class=3D"moz-txt-link-rfc2396E" = href=3D"mailto:[email protected]"><[email protected]></a> = wrote: ...</pre> </blockquote> <blockquote type=3D"cite"> <pre wrap=3D"" class=3D"moz-quote-pre">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. </pre> </blockquote> <pre wrap=3D"" class=3D"moz-quote-pre">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=3D237 write: IOPS=3D79 I'm not sure exactly what to make of that...</pre> </blockquote> I might add insult to the injury, but are you sure you need RAID-5 if it consists of just 3 drives?<br> Usually around 30% per drive's capacity will be sacrificed to hold error correction data for the array, <br> so maybe it will be much better to use 2 drives in RAID-1 (Mirror) configuration, if you need decent write performance.<br> Third drive could be used as spare device for the array, or a separate storage without = redundancy.<br></div></div></blockquote><div><br></div>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.</div><div><br></div><div>Thanks,</div><div>Casey</div></body></htm= l>= --Apple-Mail=_E5E0242D-E2CA-4760-9BCF-28826199D6F8--