setting up a RAID-1 array with a non-empty hdd?
in [Storage]
|
Prev: Any way to revive a dropped 1.5TB Seagate drive? MUST GET IT TO SPIN UP
Next: Hard drive evolution could hit Microsoft XP users
From: Arno on 10 Mar 2010 08:04 yawnmoth <terra1024(a)yahoo.com> wrote: > On Mar 9, 11:44?am, Arno <m...(a)privacy.net> wrote: >> yawnmoth <terra1...(a)yahoo.com> wrote: >> > I have a hard drive whose contents I'd like to back up. ?I was >> > thinking about using RAID-1 mirroring to do this. ?The thing I'm >> > considered about is... ?will my drive be wiped? ? >> >> Yes. >> >> > My second drive I >> > don't really care about - that drives purpose is to just serve as a >> > backup. ?But my main drive... ?I do care about that and reformating >> > would rather defeat the point. >> >> The way to do this with a decent RAID conttroller or software >> RAID is as follows: Set up a degraded RAID1 with the second >> driv. Partition it and create the filesystem. Then copy everything >> over from the first fdirve. And then add the frist drive to >> the degraded RAID1 array to get redundancy. > Any idea as to what RAID controllers might provide that > functionality? I don't know. Linux Software RAID does it and any good controller should do it, but then the question is what constitutes a good controller. > <http://www.rosewill.com/products/942/ > productDetail.htm> looked like a good RAID controller That is Fake Raid, i.e. not a RAID controller at all. I have one with the same chip, this is a plain 2 port SATA controller. What happens here is that this thing has software RAID in the BIOS, which turns out to be the wortst possible way to do RAID. Example of a real hardware controller: http://www.3ware.com/products/serial_ata2-9650.asp A bit more expensive though. > <http://www.rosewill.com/products/942/ > productDetail.htm> looked like a good RAID controller > but when I asked > them here's the response I got: > Dear Customer we can not advise you on this, your data is important > there by we cant asusre you that your cofiguration will work in this > case .we will advise create your raid separated from the drive data > then > add > drive with data as a secondary . > And I'm not even sure what that means. I have no idea either. If you add the drive with the data as secondary, any proper RAID controller will overwrite the data, and that is definitiely not what you want. >> Side note: If the data on the frist drive is important, then surely >> you have a backlup of it? > A backup is what I'm trying to create. Repeat after me: RAID is not backup. Anyways, if you are reasonably confident in your skills with handling data and the data is not reallyt important, then RAID can be used as it does at least some thing a real backup does. I would advise you to get an external USB drive, make a backup on that and then copy the data over. If you go with a Fake RAID controller (which is ok, just don't expect too much), and are doing this for the first time, the chances that you make a mistake (or the documentation is wrong or unclear, see also the bizarre answer you got) and lose all your data are just too high. As an added benefit, that gives you a means to do a proper backup. 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 10 Mar 2010 08:09 David Brown <david(a)westcontrol.removethisbit.com> wrote: > On 09/03/2010 23:47, yawnmoth wrote: >> On Mar 9, 11:44 am, Arno<m...(a)privacy.net> wrote: >>> Side note: If the data on the frist drive is important, then surely >>> you have a backlup of it? >> >> A backup is what I'm trying to create. > RAID is not a backup solution. At best, you could perhaps manage to > make a single low-level copy of your disk in this way, which is not > normally the best way to do backups, or at least not if this is your > /only/ backup (for most people, it's their data that's most important). Let me expand that a little RAID1 Backup Protects against disk failure y y Protects against PC killing disks n y (lightening, bad PSU,...) Protects against user error n y Protects against application/OS error n y Works automatically y depends The first item is why people mistake RAID1 for backup. But backup serves a few additional critical functions that RAID1 does not help with. 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: yawnmoth on 10 Mar 2010 12:21 On Mar 10, 7:04 am, Arno <m...(a)privacy.net> wrote: > yawnmoth <terra1...(a)yahoo.com> wrote: > > On Mar 9, 11:44?am, Arno <m...(a)privacy.net> wrote: > >> yawnmoth <terra1...(a)yahoo.com> wrote: > >> > I have a hard drive whose contents I'd like to back up. ?I was > >> > thinking about using RAID-1 mirroring to do this. ?The thing I'm > >> > considered about is... ?will my drive be wiped? ? > > >> Yes. > > >> > My second drive I > >> > don't really care about - that drives purpose is to just serve as a > >> > backup. ?But my main drive... ?I do care about that and reformating > >> > would rather defeat the point. > > >> The way to do this with a decent RAID conttroller or software > >> RAID is as follows: Set up a degraded RAID1 with the second > >> driv. Partition it and create the filesystem. Then copy everything > >> over from the first fdirve. And then add the frist drive to > >> the degraded RAID1 array to get redundancy. > > Any idea as to what RAID controllers might provide that > > functionality? > > I don't know. Linux Software RAID does it and any good controller > should do it, but then the question is what constitutes a good > controller. > > > <http://www.rosewill.com/products/942/ > > productDetail.htm> looked like a good RAID controller > > That is Fake Raid, i.e. not a RAID controller at all. I have > one with the same chip, this is a plain 2 port SATA controller. > What happens here is that this thing has software RAID in the > BIOS, which turns out to be the wortst possible way to do RAID. I assume BIOS software RAID is inferior to Linux software RAID just because it's likely not going to be as well written as Linux's RAID is? Anyway, thanks for the feedback!
From: yawnmoth on 10 Mar 2010 12:24 On Mar 10, 7:04 am, Arno <m...(a)privacy.net> wrote: > yawnmoth <terra1...(a)yahoo.com> wrote: > > On Mar 9, 11:44?am, Arno <m...(a)privacy.net> wrote: > >> yawnmoth <terra1...(a)yahoo.com> wrote: > >> > I have a hard drive whose contents I'd like to back up. ?I was > >> > thinking about using RAID-1 mirroring to do this. ?The thing I'm > >> > considered about is... ?will my drive be wiped? ? > > >> Yes. > > >> > My second drive I > >> > don't really care about - that drives purpose is to just serve as a > >> > backup. ?But my main drive... ?I do care about that and reformating > >> > would rather defeat the point. > > >> The way to do this with a decent RAID conttroller or software > >> RAID is as follows: Set up a degraded RAID1 with the second > >> driv. Partition it and create the filesystem. Then copy everything > >> over from the first fdirve. And then add the frist drive to > >> the degraded RAID1 array to get redundancy. > > Any idea as to what RAID controllers might provide that > > functionality? > > I don't know. Linux Software RAID does it and any good controller > should do it, but then the question is what constitutes a good > controller. > > > <http://www.rosewill.com/products/942/ > > productDetail.htm> looked like a good RAID controller > > That is Fake Raid, i.e. not a RAID controller at all. I have > one with the same chip, this is a plain 2 port SATA controller. > What happens here is that this thing has software RAID in the > BIOS, which turns out to be the wortst possible way to do RAID. > > Example of a real hardware controller:http://www.3ware.com/products/serial_ata2-9650.asp > A bit more expensive though. Also, is there a way to easily tell if an arbitrary card uses BIOS software RAID or has "real" RAID controllers? And what advantage does real RAID have over software RAID, be it Linux or BIOS? I assume less CPU usage overhead?
From: Arno on 10 Mar 2010 12:43
yawnmoth <terra1024(a)yahoo.com> wrote: > On Mar 10, 7:04?am, Arno <m...(a)privacy.net> wrote: >> yawnmoth <terra1...(a)yahoo.com> wrote: >> > On Mar 9, 11:44?am, Arno <m...(a)privacy.net> wrote: >> >> yawnmoth <terra1...(a)yahoo.com> wrote: >> >> > I have a hard drive whose contents I'd like to back up. ?I was >> >> > thinking about using RAID-1 mirroring to do this. ?The thing I'm >> >> > considered about is... ?will my drive be wiped? ? >> >> >> Yes. >> >> >> > My second drive I >> >> > don't really care about - that drives purpose is to just serve as a >> >> > backup. ?But my main drive... ?I do care about that and reformating >> >> > would rather defeat the point. >> >> >> The way to do this with a decent RAID conttroller or software >> >> RAID is as follows: Set up a degraded RAID1 with the second >> >> driv. Partition it and create the filesystem. Then copy everything >> >> over from the first fdirve. And then add the frist drive to >> >> the degraded RAID1 array to get redundancy. >> > Any idea as to what RAID controllers might provide that >> > functionality? ? >> >> I don't know. Linux Software RAID does it and any good controller >> should do it, but then the question is what constitutes a good >> controller. >> >> > <http://www.rosewill.com/products/942/ >> > productDetail.htm> looked like a good RAID controller >> >> That is Fake Raid, i.e. not a RAID controller at all. I have >> one with the same chip, this is a plain 2 port SATA controller. >> What happens here is that this thing has software RAID in the >> BIOS, which turns out to be the wortst possible way to do RAID. > I assume BIOS software RAID is inferior to Linux software RAID just > because it's likely not going to be as well written as Linux's RAID > is? Basically: No suport for RAIDed partitions, very basic admin tools, etc.. May still be ok for lower requirements. And althoigh most of these do not state Linux support, the Linux dm-raid driver is often able to access them under Linux as well. > Anyway, thanks for the feedback! No problem. -- 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 |