From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrei Banu Subject: Re: raid1 - ssd, doubts Date: Tue, 30 Sep 2014 18:46:52 +0300 Message-ID: <542AD06C.9080908@redhost.ro> References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Roberto Spadim , Linux-RAID List-Id: linux-raid.ids Hi, I am in no way of the same technical caliber as many of the people on this list so please take my advice with a grain of salt. However I do have some experience with Samsung SSDs in RAID 1 software (md-raid) and I would like to warn you against it. My setup is with 840 PROs of 512GB. I did leave free space (not partitioned) for OP. The SSDs are connected on SATA3. I'll give you the result of 2 tests and if you are happy, go ahead: READ root [~]# hdparm -t /dev/sda /dev/sda: Timing buffered disk reads: 292 MB in 3.01 seconds = 96.92 MB/sec WRITE root [~]# dd if=/dev/zero of=testn bs=4k count=256k conv=fdatasync 262144+0 records in 262144+0 records out 1073741824 bytes (1.1 GB) copied, 13.4047 s, 80.1 MB/s When the setup is fresh you'll get significantly more out of it but after a while (this setup is roughly 1 year old) this is what you get with Samsung SSDs in RAID1 SW. At least this is my experience and I did try to improve it. As a matter of fact, before making a secure erase of one of the SSDs the write speed was under 10MB/s. What you see above is a lot better than what it started out (but it's true that after the secure erase the read/write speeds were a lot better but it dropped in a very short time frame). A few points: 1. CAUTION: 840 EVO are proved to have a read speed degradation for old data written to the drive (this is unrelated to RAID but it probably affects performance in RAID). 2. I believe that any SSDs, regardless of the brand, in a software RAID-1 setup might be a bad idea. 3. I believe that the same SSDs in a hardware RAID setup might lead to a different story. Again: I am not a technical wiz (like many of the people on this list) but I did have some experience with this so I thought I should let you know. Kind regards! On 30.09.2014 17:50, Roberto Spadim wrote: > hi guys! > i will use a ssd raid1, i want know if raid1 trim is supported at mdadm > i will use a 840 evo (or evo pro not selected the right one yet) 500gb > each, raid1, today database size is 100gb, i think it will grow > 10gb/year, i had many space... > > the point are: madm raid1 trim is supported? or should i use lvm? > should i partition it with 400gb and leave 100gb untouched? or should > i use a hdd+ssd and dmcache? > > > :) thanks guys, that's a small enterprise solution, they can't buy > raid cards and sas harddisk are same price of ssd :) > > any idea/experience and information is wellcome > >