Date: Mon, 4 Mar 2013 19:38:02 +1100 From: Peter Jeremy <peter@rulingia.com> To: Don Lewis <truckman@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: access to hard drives is "blocked" by writes to a flash drive Message-ID: <20130304083802.GA44865@server.rulingia.com> In-Reply-To: <201303040712.r247CejP008718@gw.catspoiler.org> References: <20130304053547.GY2930@kib.kiev.ua> <201303040712.r247CejP008718@gw.catspoiler.org>
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--3MwIy2ne0vdjdPXF Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2013-Mar-03 23:12:40 -0800, Don Lewis <truckman@freebsd.org> wrote: >On 4 Mar, Konstantin Belousov wrote: >> It could be argued that the current typical value of 16MB for the >> hirunningbufspace is too low, but experiments with increasing it did >> not provided any measureable change in the throughput or latency for >> some loads. > >The correct value is probably proportional to the write bandwidth >available. The problem is that write bandwidth varies widely depending on the workload. For spinning rust, this will vary between maybe 64KBps (512B random writes) and 100-150MBps (single-theaded large sequential writes). The (low-end) SSD in my Netbook also has about 100:1 variance due to erase blocking. How do you tune hirunningbufspace in the face of 2 or 3 orders of magnitude variance in throughput? Especially since SSDs don't gradually degrade - they hit a brick wall. --=20 Peter Jeremy --3MwIy2ne0vdjdPXF Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iEYEARECAAYFAlE0XWoACgkQ/opHv/APuIeHbACcCk/rPZvdWOaw39O04JSSk131 WZsAn1uwrzYpq9e+yPGGdfsz6a4rtRuC =MVQ7 -----END PGP SIGNATURE----- --3MwIy2ne0vdjdPXF--
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