From mboxrd@z Thu Jan 1 00:00:00 1970 From: pg@lxra2.for.sabi.co.UK (Peter Grandi) Subject: Re: Intel SSD or other brands Date: Thu, 29 Dec 2016 17:33:17 +0000 Message-ID: <22629.18653.431222.163351@tree.ty.sabi.co.uk> References: <0329d841-984b-fa25-0bf2-0aba4d55b6de@websitemanagers.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Linux RAID List-Id: linux-raid.ids > [ ... ] sync=1 really differentiates drives and you really > find which drives are better. [ ... ] It is not necessarily "better" in a strict sense: flash SSD devices with supercapacitor-backed persistent caches can be much faster on 'fsync' heavy workloads, but also cost a lot more (probably mostly because of market segmentation). Of course especially on a RAID5 set with lots of read-modify-write. It is a different performance envelope, not necessarily a "better" one. If one does not need small-write speed then cheaper drivers are more appropriate. However devices which don't have persistent caches and still have high 'sync=1'/'direct=1' speed because they don't implement 'fsync' synchronously are definitely worse, in the sense of having arguably no performance at all. Some manufacturers think that using an SLC cache helps without a persistent-ed RAM cache, but the persistent=-ed RAM seems a lot better to me.