RAID1: Read-prefer one disk?
in [Setup]
|
Prev: Lew Pitcher
Next: root password
From: Arno on 5 Jul 2010 10:55 Does anybody know whether it is possible to configure an md RAID1 to read with preferrence from one particular RAID disk? The reasom I ask is that I have an application that does very ver writes but a lot of small file reads. I would like to put that on a RADI1 consiting of an SSD and a conventional partition, but that makes only sense if I can tell the kernel to read with a high level of preferrence from the SSD. (Regular RAID consistency checks and SMART checks for the HDD are in place.) Thanks for any insight. If nobody knows, I will probably go for hourly manual mirroring via rsync/rdiff-backup or the like to HDD, but that is sort of kludgy... Arno -- Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno(a)wagner.name GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F ---- Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans
From: David Brown on 5 Jul 2010 13:27 Arno wrote: > Does anybody know whether it is possible to configure an > md RAID1 to read with preferrence from one particular > RAID disk? The reasom I ask is that I have an application > that does very ver writes but a lot of small file reads. > I would like to put that on a RADI1 consiting of an SSD > and a conventional partition, but that makes only sense > if I can tell the kernel to read with a high level of > preferrence from the SSD. (Regular RAID consistency > checks and SMART checks for the HDD are in place.) > > Thanks for any insight. > > If nobody knows, I will probably go for hourly manual > mirroring via rsync/rdiff-backup or the like to HDD, > but that is sort of kludgy... > If you are using mdadmin for your raid, you can specify one or more devices as "--write-mostly" which means they will not be read unless it's necessary. If you include a write-intent bitmap, then you can also build up a queue of writes to the write-mostly disk(s) without hindering performance of the array. It's really aimed at mirroring over slower links (such as for an external iSCSI drive over a longer distance link), but I'd imagine it would work fine for your purposes. If you try out that idea, let us know your results - I'm curious as to how well it works. <http://linux.die.net/man/8/mdadm>
From: Arno on 5 Jul 2010 14:04 David Brown <david.brown(a)hesbynett.removethisbit.no> wrote: > Arno wrote: >> Does anybody know whether it is possible to configure an >> md RAID1 to read with preferrence from one particular >> RAID disk? The reasom I ask is that I have an application >> that does very ver writes but a lot of small file reads. >> I would like to put that on a RADI1 consiting of an SSD >> and a conventional partition, but that makes only sense >> if I can tell the kernel to read with a high level of >> preferrence from the SSD. [...] > If you are using mdadmin for your raid, you can specify one or more > devices as "--write-mostly" which means they will not be read unless > it's necessary. If you include a write-intent bitmap, then you can also > build up a queue of writes to the write-mostly disk(s) without hindering > performance of the array. Thanks, that is what I was looking for. > It's really aimed at mirroring over slower links (such as for an > external iSCSI drive over a longer distance link), but I'd imagine it > would work fine for your purposes. > If you try out that idea, let us know your results - I'm curious as to > how well it works. Will do. I need to move my SSD for that, could take a few days. Arno -- Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno(a)wagner.name GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F ---- Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans
From: Arno on 6 Jul 2010 19:54 Arno <me(a)privacy.net> wrote: > David Brown <david.brown(a)hesbynett.removethisbit.no> wrote: >> Arno wrote: >>> Does anybody know whether it is possible to configure an >>> md RAID1 to read with preferrence from one particular >>> RAID disk? The reasom I ask is that I have an application >>> that does very ver writes but a lot of small file reads. >>> I would like to put that on a RADI1 consiting of an SSD >>> and a conventional partition, but that makes only sense >>> if I can tell the kernel to read with a high level of >>> preferrence from the SSD. > [...] >> If you are using mdadmin for your raid, you can specify one or more >> devices as "--write-mostly" which means they will not be read unless >> it's necessary. If you include a write-intent bitmap, then you can also >> build up a queue of writes to the write-mostly disk(s) without hindering >> performance of the array. > Thanks, that is what I was looking for. >> It's really aimed at mirroring over slower links (such as for an >> external iSCSI drive over a longer distance link), but I'd imagine it >> would work fine for your purposes. >> If you try out that idea, let us know your results - I'm curious as to >> how well it works. > Will do. I need to move my SSD for that, could take a few days. Just posted as "RAID1: HDD+SDD -- some benchmarks" in this newsgroup. Arno -- Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno(a)wagner.name GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F ---- Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans
|
Pages: 1 Prev: Lew Pitcher Next: root password |